CHAPTER XXXI

THE ORIGIN AND THE FORMS OF MOUNTAINS

=A mountain defined.=—As ordinarily understood, mountains are elevations upon the earth’s surface which rise above the general level of the country. Their summits need not be at great heights above the sea, but it is essential that they project above the average level of the surrounding country by at least a quarter of a mile. Lower elevations are described as hills. On the other hand, the elevation of a plateau like the “High Plains” of the western United States may be as much as a mile, but the vast expanse of nearly level surface precludes the use of the term “mountain.” The word is thus applied to a feature of the earth and not merely to an elevated tract.

In a collective sense, though more often in the plural form, the term is properly applied to groups of similar features which have a common origin in local uplift of the land. The origin of mountains used in this sense of mountain complexes is thus connected with some essentially local uplift of the earth’s surface. This may take place by the processes of folding and superincumbent fault displacement, by volcanic extravasations or ejections, or by a deeper seated and essentially hydrostatic elevation of rock beds over molten rock material.

The existing _forms_ of mountains, as we are to see, are largely shaped by the erosional processes which are set in operation by the uplift itself, though often completed long subsequent to it.

=The festoons of mountain arcs.=—From our earliest studies of school geographies, we have become familiar with the arrangement of the more important mountains in long chains or systems. Comparatively few persons have given any further attention to the arrangement of the chains, though over large areas of the earth’s surface the distribution of mountain ranges is deeply significant. The map of Asia in particular presents a series of great sweeping arcs or crescents which are grouped as though hung upon the map in festoons with knots or vertexes to separate neighboring groups (Fig. 474, p. 438, and Fig. 472).

The significance of these mountain groupings in the evolution of the earth’s surface has been pointed out by the great Viennese geologist Suess, to whom we are indebted for focusing upon the plan of the earth an amount of attention which before had been largely given to the preparation of hypothetical sections of strata which were largely buried from sight beneath the earth’s surface. Broadly speaking, the mountain arcs may be said to be grouped about those shields of older rock which geological studies have shown to be the oldest land masses upon the globe. Within the northern hemisphere these original continents are represented by the areas of crystalline rock centered over Hudson Bay, the Baltic Sea, and an area in northeastern Siberia known to geologists as Angara Land. In our study of the figure of the earth (Chapter II) it was found that these shields represent the truncated angles of the rounded tetrahedral form toward which the planet is tending (Fig. 3, p. 12).

=Theories of origin of the mountain arcs.=—The mountain arcs, when studied in detail, are found to be composed of closely folded rock strata, the flexures of which are generally so overturned that their axial planes dip toward the center of the arc (Fig. 473). It was the view of Suess that these arcs are to be explained by a pushing outward of the rock strata from the center of the arc toward its periphery, thus causing a wrinkling of the surface strata and an overriding of the surrounding formations, which upon this hypothesis opposed a greater resistance to the sliding movement. The folding together of the strata due to the sliding naturally involves a very considerable diminution of the surface area presented by the strata (Fig. 22, p. 42). In the case of the Alpine chains it has been estimated that a flat land area, four hundred to eight hundred miles across, has by the folding process been reduced to a width of only about one hundred miles, or from a fourth to an eighth of its former width.

The weakness of Professor Suess’ theory lies in the fact that such compression as it implies is assumed to be due to an _outward_ movement of the relatively small area of the earth’s outer shell which is included _within_ the arc. It must be obvious that such a movement, being from a center toward three sides at once, would for this circumscribed area involve enormous proportionate reduction in superficial area of the strata and could only result in a hiatus near the center of the arc. No such gap is to be found, and one would, moreover, be difficult to account for upon any plausible hypothesis. On the other hand, the general contraction of the planet as a whole, involving as it does reduction of surface over large areas, is a well-recognized fact; and if it be true that the shields formed by the older continents are less subject to contraction than the remaining portions of the surface, it is easy to understand why the earth’s outer skin should be wrinkled by _underfolding_ and thrusting about these continental margins. The contrast of this view with that of Professor Suess is expressed in the diagrams of Fig. 473.

We may illustrate this conception by a stretched sheet of rubber cloth such as is in common use by dentists, upon which a thin layer of hot Canada balsam has been spread. This substance congeals upon cooling to near-normal temperatures, and if a small local area of the balsam layer be chilled and the tension upon the rubber then released, the viscous balsam of the unchilled portion of the layer is thrown into wrinkles about the cooled and more resistant areas. These more resistant portions of the stratum may thus represent the ancient continental shields of our planet.

=The Atlantic and Pacific coasts contrasted.=—In his studies of mountain arcs in their relation to the plan of the earth, Professor Suess has shown how the arrangements of the mountain chains about the two larger oceans represent two strongly contrasted types. Whereas about the Pacific margin the mountain arcs are, as it were, strung in festoons which trend parallel to and are convex toward the coast, or else lie in fringing garlands of islands in the same attitude (Fig. 474); the mountain chains about the Atlantic become sharply truncated as they reach the coast, and thus indicate that the basin of this ocean has been produced by an inthrow or depression between great marginal displacements in some period subsequent to the formation of the mountains.

Thus the mountain folds of the Appalachian system are in Newfoundland cut off abruptly at the coast line, and the same beds, similarly truncated, are encountered again across the expanse of ocean in the folds at the coast of western Europe (Fig. 475). In discontinuous remnants this ancient mountain chain may be traced in an east and west direction across western and central Europe. We have thus here to do with a single mountain system which extends from central Europe to northern Alabama, out of which a great link has been taken by the subsequent sinking in of the basin of the Atlantic Ocean.

=The block type of mountain.=—The inclusion of most elevations in mountain chains and arcs is one of the most obvious facts to any one who has examined world atlases with this subject in mind. Such chains are almost invariably composed of folded rocks, thus indicating that erosion has removed great superincumbent masses of strata since the crustal compression produced the folds at considerable depths below the then surface.

There are, however, large elevated tracts upon the earth’s surface which are intersected by deep valleys, but where no arrangement of the elevated portions within chains or ranges is to be detected. In such cases the distribution of mountain and valley may bear a resemblance to a mosaic of disturbed parts which stand at different levels (Fig. 476).

Such block mountain districts are to be found in many parts of the earth’s surface, but notably within the Great Basin of the western United States, and in the land area which borders the Indian Ocean upon the west and northwest. In contrast with the mountain arcs, so strikingly exemplified by the continent of Asia as a whole, its extreme southwestern portion is made up of an alternation of plateau and rift valley separated from each other by great displacements. Though modified to some extent by erosion, the elevations seem generally to represent the displaced crust blocks which in mutual adjustments have been left at the highest levels (Fig. 477). The valley of the Jordan, with the mountains of Lebanon rising above it, is near the northern extremity of this faulted mountain region (Fig. 434, p. 404), while the Great Rift valley, crossing east Central Africa, and the many neighboring rifts to the east and west, are graven in lines so deep that an observer upon a neighboring planet might perhaps detect them.

It is not necessary in all cases to assume that the block mountains of a faulted district represent the blocks which in the adjustments were left the highest. Erosion in the course of time accomplishes marvels of transformation, and it may result that heavy masses of more resistant rock eventually project the highest, even though they may represent the downthrown blocks in the fault mosaic (Fig. 43, p. 60).

Where in addition to undergoing changes of level the earth blocks have been tilted, the features long since described from our western interior basin as “Basin Range structure” are developed. Here the upper surface of the disturbed earth blocks betrays the evidence of a definite tilt in some one direction (Fig. 478, and Fig. 431, p. 402).

=Mountains of outflow or upheap.=—An important type of mountain, generally described as volcanic, may be due either to the outflow of lava at the earth’s surface, or to accumulations of separated fragments of lava, first thrown into the air, and then deposited by gravity or admixed with water as volcanic mud. Such mountains, both before and after modification by erosion, assume the strikingly characteristic forms which have been fully discussed in Chapters IX and X. The dominant types are the lava dome and the puy, the cinder cone, and the more complex composite cone. Excepting only the surface produced by the few great fissure eruptions and the semivolcanic mesa type, the individual mountains of volcanic origin develop features with notably circular bases.

=Domed mountains of uplift—laccolites.=—At a considerable number of widely separated localities upon the earth’s surface, mountainous regions are encountered, the central areas or cores of which are composed of intrusive igneous rock such as granite, and about this core the sediments dip away in all directions as though they had once formed a continuous roof above it and had been forced into this dome by hydrostatic pressure of the once viscous material beneath (Fig. 152, p. 143, and Figs. 479 and 480). Examples of such domed mountains of uplift were first described by Gilbert from the Henry Mountains of Utah, but instances are furnished by many elevated tracts, especially within the western United States. Such mountains are known as _laccolites_, but when one margin at least of the igneous core corresponds to a displacement, the mountain is described as a _bysmalite_ (Fig. 481).

When subjected to long-continued erosion, the generally fissured granitic core of the laccolite weathers in a wholly different manner from the bedded sediments which surround and still in part mount over it. The former usually presents a more or less jagged surface which contrasts sharply with the gently sloping tables of the latter (Fig. 479). About the high granite core of the mountain, the several strata of the uptilted formations present each a steep slope toward this higher land, and a gentler slope in the opposite direction. Such unsymmetrical ridges which surround the mountain area are often referred to as “hog backs” (plate 12 B). The arrangement of the strata in the hog backs thus presents an overlapping series like the shingles upon a roof, except that the overlapping is here from the bottom instead of the top, and the exposed ends thus face toward the crest. Unlike a shingle roof the hog backs do not shed the water which descends to them from the higher levels, but, on the contrary, they cause it to flow in troughs parallel to the base of the slope except where outlets are found through them.

=Mountains carved from plateaus.=—In the mountain types thus far discussed, the local uplifting of the land has itself developed features which in the aggregate may be referred to as mountains, even though the characters of the original surface are soon destroyed by erosive processes of one sort or the other. Erosive processes are, however, quite competent to produce mountain forms from a featureless plateau, and particularly through the incision by streams of running water, the best studied process of mountain sculpture (see Chapters XI-XIII). This process of throwing valleys about an elevated section of the earth’s surface, and so carving out mountains, is sometimes described as _circumvallation_; and if the term “mountain” be applied in its ordinary sense to describe an individual feature, it is clear that most mountains have been formed in this way.

To discuss the characteristic shapes of such mountains would be largely to review the contents of this book, and especially those portions which discuss the character profiles resulting from the action of each sculpturing or molding agent. The work of frost and other weathering agencies, of running water, of mountain and of continental glacier, would all have to be considered in order to evolve the history of each mountain.

In addition to discovering the agents which were chiefly responsible for the shaping of the mountain, we may, further, in many cases determine at what stage the work of one agent has been succeeded by that of another, and at least at what stage of its complete cycle of activity the latest agent is now at work.

=The climatic conditions of the mountain sculpture.=—Since the different geological agencies operate either in a different manner or with differences in vigor according to the varying climatic conditions, the mountains of arid regions may in most cases be readily differentiated from those of the more habitable humid sections of country. In broad lines these differences may be summed up in the greater prevalence of the curving line within the landscapes of humid districts. This may be largely ascribed to the influence of the mat of vegetation, which protects the rock surface from more rapid mechanical degeneration, and arrests the sliding movements within the already loosened rock débris. In place of the reversed curves of the lines of beauty, so generally observed in the landscapes of well-watered regions, the desert lands present ever a repetition of the vertical cliff alternating with a sort of many gabled façade which is occasionally due to truncation of mountain spurs by the waves of former lakes, but far more often the outlines of débris cones built up beneath each prominent joint of the cliff walls (Fig. 482).

=The effect of the resistant stratum.=—In a striking manner mountain landscapes may disclose the influence of the diversified rock materials and of the rock structures as well. After prolonged erosion there is likely to be little correspondence between the positions of the anticlinal folds and the crests of the higher mountains. Such mountains are, in fact, much more likely to rise over synclines than upon the site of anticlines. The traveler who enters the Alps by any of the several railways, or who journeys by steamer over the beautiful lake of Lucerne, has a most favorable opportunity to study the position of the rock folds in the mountain sections that are unrolled in succession before him. Rarely indeed will he find a definite anticline in correspondence with a mountain peak, for the layers which are most resistant have developed the peaks, and it is because the outer layers of the anticlines open by local tension (see Fig. 26, p. 45) that they were first cut away by erosion, so that the hard layers within the synclines are likely to constitute the peaks within the existing surface.

When, as sometimes happens, an older and likewise more resistant bed has been folded back upon younger and softer formations, an isolated remnant may be found “unrooted” to its base, upon which it appears as though floating within a billowy sea of the softer formations (Fig. 483).

=The mark of the rift in the eroded mountains.=—Applying the term “mountain” in its collective sense for a circumscribed area of uplifted crust, whether represented to-day by a folded or a faulted complex, a lava mass, or a granite dome; the period of uplift has marked the beginning of the activity of sculpturing agencies. By these the mass is pared down as it is shaped into a more or less intricate design of component and essentially repeating units. In the vernacular the word “mountain” is applied to these units into which the larger mountain mass is subdivided.

It has been one of the main objects of this work to point out that the peculiar shapes of these elementary mountains are each characteristic of the erosive agents which produced them, and that each surface has marks which may be recognized in those lines of profile which recur within the landscape—the character profiles. In the subdivision of the larger mass—the _genetical_ mountain—to form the numerous smaller masses—the _erosional_ or _circumvallational_ mountains—there is disclosed a pattern of fractures which has guided the erosional agents in their incisional operations (see Chapter XVII). In high altitudes, where the action of frost is so potent in prying at the wider fractures, this subdivision of the mass may be revealed by the sculpturing of squared towers or battlements (Fig. 484).

For other examples in which the sculptured surface is largely the handiwork of a single erosional agent, as over vast areas in the Canadian wilderness, the revelation of the fracture design is no less apparent. Here a series of crystalline rocks underlie broad expanses of territory and are without noteworthy variations of hardness and almost bare of surface débris. Sculptured beneath a mantling ice sheet, excavation has naturally been concentrated above the more widely gaping fissures of the joint-fault system, doubtless already marked out in the river network which the glacier overrode. The result has been a division of the surface into a series of low, oval ridges or hummocks, which over vast areas are repeated with monotonous regularity. Wherever the lower levels have been flooded, symmetrical low islands of nearly uniform elevation rise from the expanse of water and may be counted by thousands. Though the smaller islands have notably regular shore lines, the larger ones disclose their composition from smaller units by the breaking of their shores into similar bays spaced with regular intervals (Fig. 485, and Figs. 243 and 245, p. 229).

The ever repeating fracture design of the earth’s crust is not restricted to the mountain masses which it has broken up, and the unity of which it has done so much to conceal. It extends far outside the margin of these masses, and is in fact common to whole continents and perhaps even to the planet as a whole. The part played by this design of fractures in the control of the sculpture of landscapes it would be hard to overestimate. Through its influence the striking features molded by one agent have been merged in the contrasted shapes developed by another. It is the great outline blender in the creation of nature’s masterpieces of form and color. Thus the lines of this mysterious fracture network, though stamped in indelible characters upon our landscapes, are generally lost in the ensemble effect and may long remain undiscovered. Like a moss-grown inscription upon a slab of marble, though veiled, it may yet be deciphered; and if the veil be withdrawn, the runic characters are disclosed, and one of nature’s laws lies open before us.

READING REFERENCES FOR CHAPTER XXXI

Mountain arcs or festoons:—

ED. SUESS. The Face of the Earth, vol. 2, 1906, pp. 201-207; vol. 4, 1909, pp. 498-542.

Block mountains:—

G. K. GILBERT. Surveys West of the 100th Meridian (Wheeler), vol. 3, Geology, Washington, 1875, Pt. 1, pp. 19 _et seq._, 48.

J. W. POWELL. Report on the Geology of the Eastern Portion of the Uinta Mountains and a Region of Country Adjacent thereto, U. S. Geol. and Geogr. Surv. Ter., II Div. Washington, 1876, pp. 218.

JOHN W. GREGORY. The Great Rift Valley. London, 1896, pp. 422.

Laccolites and bysmalites:—

G. K. GILBERT. Report on the Geology of the Henry Mountains, U. S. Geol. and Geogr. Surv. Ter., 1877, pp. 18-98.

WHITMAN CROSS. The Laccolitic Mountain Groups of Colorado, Utah, and Arizona, 14th Ann. Rept. U. S. Geol. Surv., 1895, pp. 157-241, pls. 7-16.

W. H. WEED and L. V. PIRSSON. Geology and Mineral Resources of the Judith Mountains of Montana, 18th Ann. Rept. U. S. Geol. Surv., Pt. iii, 1898, pp. 485-556, pl. 75.

W. H. WEED. Geology of the Little Belt Mountains, Montana, etc., 20th Ann. Rept. U. S. Geol. Surv., Pt. iii, 1900, pp. 387-400.

VERA DE DERWIES. Recherches géologiques et pétrographiques sur les loccolithes des environs de Piatigorsk (Caucase du Nord). Geneva, 1905, pp. 84, pls. 3.

R. A. DALY. The Mechanics of Igneous Intrusion, Am. Jour. Sci. (4), vol. 15, 1903, pp. 269-278; vol. 16, 1903, pp. 107-126.

JOSEPH BARRELL. Geology of the Marysville Mining District, Montana. A study of Igneous Intrusion and Contact Metamorphism. Prof. Pap. 57, U. S. Geol. Surv., 1907, pp. 151-178.

Climatic condition in relation to land sculpture:—

C. E. DUTTON. Tertiary History of the Grand Canyon District, Mon. 2, U. S. Geol. Surv., 1882, pp. 264, pls. 42.

APPENDIX A

THE QUICK DETERMINATION OF THE COMMON MINERALS

Before one may gain a knowledge of rocks or the architecture of their arrangement within the earth’s crust, it is quite essential that some familiarity should be acquired with the appearance and properties of the commonest minerals, and particularly those which enter as essential constituents into the more abundant rocks. To be a competent mineralogist, one must have a rather extended knowledge both of inorganic chemistry and of the science of crystallography, which, fascinating as it is to study, involves some technical knowledge of mathematics and much laboratory experience. Though necessary to any one who contemplates making a career as a geologist, this special study is not essential to a cultural course like the present one. The attempt will here be made to bring together a body of fact, from the study of which the student may quickly learn to recognize the commonest minerals in their usual varieties. The tests he is to apply are mainly physical, and in place of an elaborate discussion of crystal symmetry, pictures only can be supplied.

To the beginner the usual textbook of mineralogy is difficult to read intelligently, for the reason that for each mineral species it sets before him a catalogue of each physical property in its turn, with little indication of those data which in the individual case have special diagnostic value. None the less, however, the student is advised to consider the several properties of each mineral in a definite order, and the following may serve as well as any: crystal or other form, cleavage, fracture, luster, color, streak, transparency, tenacity, hardness, magnetism, and specific gravity. In endeavoring to connect the specific values of these properties with individual mineral species, the chemical composition and the manner of occurrence are not to be forgotten. It is well for the student to be supplied with a small pocket lens and with a pocket knife the blade of which has been magnetized.

=Crystal form.=—Some mineral species generally occur in more or less definite crystals—are bounded by definite plane surfaces developed when the mineral was formed; others in groups of interfering crystals or aggregates, in which case the mineral is said to be crystalline; while still others are rarely found crystallized at all. Thus in a given case crystal form may, or may not, be important for the diagnosis of the substance. If a mineral species is usually to be found in crystals, the student should be aware of the fact, and if possible should have a mental picture of the common crystal shape or shapes. Without an extended knowledge of crystallography, this must be supplied him by drawings. Since crystals of most species are apt to be distorted, owing to the fact that some planes within the same group appear upon the crystal with a larger development than others, it is convenient to remember that markings, such as lines or etchings upon the crystal faces, are the same throughout the same group of planes, and in the text figures such groups of planes are indicated by the use of a common letter. For crystalline aggregates such terms as fibrous, radiating, massive, or granular have their usual meanings.

=Cleavage.=—It is characteristic of most crystals that they break or _cleave_ along certain directions so as to leave plane or nearly plane surfaces, and the luster of the cleaved surface measures the perfection of the cleavage property. It is important always to note how many such directions of cleavage are present, and, roughly at least, at what angles they intersect—whether they are perpendicular to each other or inclined at some other angle. Further, it should be noted whether a given cleavage is _perfect_, that is, easy, which will be indicated by the thinness of the plates which can be secured. An extremely perfect cleavage is possessed by the mineral mica, whose plates are thinner than the thinnest paper. In the case of imperfect or interrupted cleavage, the fracture surfaces are not plane throughout, but interrupted, the surface “jumping” from one plane to a neighboring parallel one. It is especially important to note whether, in the case of several cleavages possessed by a crystal, all have the same degree of perfection, or whether they exhibit differences.

=Fracture.=—In minerals with poorly developed cleavage, the fracture surface is described as _fracture_. Fracture is thus perfect in proportion as cleavage is imperfect. The fracture is described as conchoidal when it shows waving spherical surfaces like broken glass. For fine aggregates the fracture is described as even, uneven, earthy, etc., names which are generally intelligible.

=Luster.=—This term is applied especially to the manner in which light is reflected from mineral surfaces. The most important distinction is made between those minerals which have a _metallic_ luster and those which have not, the former being always opaque. Other characteristic lusters are adamantine (like oiled glass), vitreous (glassy), resinous, waxy, etc.

=Color.=—For minerals which possess metallic luster the color is always practically the same, and hence it becomes a valuable diagnostic property. Of minerals which have nonmetallic luster, the color may be always the same and hence characteristic, but in the case of many minerals it ranges between wide limits and sometimes runs almost the entire gamut of hues, yet without appreciable changes in the chemical composition of the mineral.

=Streak.=—This term is applied to the color of the mineral powder, and is usually fairly constant, even when the surface color of different specimens may vary within wide limits. In the case of fairly soft minerals the streak is best examined by making a mark on a piece of unglazed porcelain (streak stone).

=Transparency= (=diaphaneity=).—The terms “transparent”, “translucent”, “subtranslucent”, and “opaque” are used to describe decreasing grades of permeability by light rays. Through transparent bodies print may be read, while translucent bodies allow the light to be transmitted in considerable quantity through them, though without rendering the image of objects.

=Tenacity.=—This comprehensive term includes such properties as brittleness, flexibility, elasticity, malleability, etc.

=Hardness.=—Quite erroneous notions are held concerning the meaning of this very common word, which properly implies a resistance offered to abrasion. It is one of the most valuable properties for the quick determination of minerals, since minerals range from diamond upon the one hand—the hardest of substances—to talc and graphite, which are so soft as to be deeply scratched by the thumb nail. For practical purposes it is sufficient to make use of a rough scale of hardness made up from common or well-known minerals. If we exclude the gem minerals, this scale need include but seven numbers, which are: talc, 1; gypsum, 2; calcite, 3; fluor spar, 4; apatite, 5; feldspar, 6; and quartz, 7. A given mineral is softer than a mineral in the scale when it can be visibly scratched by a scale mineral, but will not leave a scratch when the conditions are reversed. If each will scratch the other with equal readiness, the two minerals have the same hardness.

Since it may often be desirable to test mineral hardness when no scale is at hand, the following substitutes may be made use of: 1, greasy feel and easily scratched by the thumb nail; 2, takes a scratch from the thumb nail, but much less readily; 3, scratched by a copper coin and very easily by a pocket knife; 4, scratched without difficulty by a knife; 5, scratched with difficulty by a knife, but easily by window glass; 6, scratched by window glass; 7, scratches window glass with readiness, but a grain of sand may be substituted to represent quartz in the scale.

=Magnetism.=—Though nearly all minerals which contain important quantities of the elements iron, cobalt, or nickel may be attracted to a strong electromagnet, there are but two common minerals, and these of widely different appearance, whose powder is lifted by a common magnet. Others are, however, lifted after strong heating in the air (_ignition_), and this is a valuable test.

=Specific gravity.=—Rough tests of relative weight, or specific gravity, may be made by lifting fair-sized specimens in the hand. Better determinations require the use of a spring balance.

=Treatment with acid.=—The carbonate minerals react with warm and dilute mineral acid so as to give a boiling effect (effervescence), since carbonic acid gas escapes into the air in the process.

PROPERTIES OF THE COMMON MINERALS

The more important common minerals fall into two classes according as they have large economic importance as ores, or enter in an important way into the composition of rocks.

I. The Minerals of Economic Importance

=Hematite.=—The sesquioxide of iron, Fe_{2}O_{3}, and by far the most important ore of iron. Rarely in good crystals, but sometimes in thin opaque scales bearing some resemblance to mica and known as micaceous or specular iron ore. At other times in nodules built up from radial needles (needle ore); in hard masses mixed with fine quartz grains (hard hematite); or in soft reddish brown earth (soft hematite). Color, black to cherry red. The powdered mineral always cherry red or reddish brown, and easily lifted by the magnet after ignition. Hardness 5.5-6.5; specific gravity 5.

=Magnetite.=—The magnetic oxide of iron, Fe_{3}O_{4}, often in crystals like Fig. 486, ^{1-2}. Black and opaque with a metallic luster. Streak black. Lifted by a magnet and sometimes itself capable of lifting filings of soft iron (lodestone). Hardness 5.5-6.5. Specific gravity 5.

=Limonite.=—The most abundant and most valuable of the hydrated iron ores, 2 Fe_{2}O_{3}. 3 H_{2}O. Chemical composition the same as iron rust, with which in the earthy form it is identical. Never in crystals, but often in mammillary or rounded pendant forms resembling icicles, or sometimes clusters of grapes. Its yellow (rust) streak is its best diagnostic property. Ignited it gives off water and becomes magnetic. The streak and its notably lower specific gravity distinguish it from certain forms of hematite which it outwardly resembles. Hardness 5-5.5. Specific gravity 3.6-4.

=Pyrite, iron pyrites, or “fool’s gold.”=—The sulphide of iron, FeS_{2}. The most widely distributed sulphide mineral and now a chief source of the great chemical reagent, sulphuric acid or vitriol. Often, but not always, in crystals (Fig. 486, ^{3-5}) which have peculiar striæ upon their faces. At other times the mineral is found massive or in radiated needles. Bright metallic luster with the color of new brass, though often tarnished or altered upon the surface to limonite. Hard and brittle, and so distinguished from gold, which is soft and malleable and of the color of the paler old brass (which contained a larger percentage of zinc). Gold is, further, about four times as heavy as pyrite. Hardness 6-6.5. Specific gravity 5.

=Chalcopyrite, copper pyrites.=—A mixed sulphide of copper and iron. If in crystals, like Fig. 486, ^6; otherwise massive or compact. Luster metallic. Color orange-yellow, often with local blue and green iridescence like a pigeon’s throat. Distinguished from pyrite by the deeper color and lower hardness, and from gold, particularly, by its brittleness and lower specific gravity. Hardness 3.5-4. Specific gravity 4.

=Galenite, galena.=—Sulphide of lead, PbS. The chief ore of lead, and, from admixture of a silver mineral, of silver as well. Usually found in crystals (Fig. 486, ^7). Always cleaves into blocks bounded by six very perfect rectangular faces which, when freshly broken, show a bright silvery luster and quickly tarnish to a peculiarly “leaden” surface. Very heavy. Color and streak lead-gray. Hardness 2.5. Specific gravity 7.5.

=Sphalerite, zinc blende.=—Sulphide of zinc, ZnS, usually with considerable admixture of sulphide of iron. The great ore of zinc. Not infrequently in crystals (Fig. 486, ^{8-9}), but more often in cleavable crystalline aggregates. The cleavage in fine aggregates is sometimes difficult to make out, but in coarse-grained masses it is seen to be equally and highly perfect in six different directions, so that a symmetrical twelve-faced form may sometimes be broken out (dodecahedron). Luster like that of rosin (rosin jack), though when with large iron admixture the color may approach black (black jack). The lighter colored varieties are translucent. Hardness 3.5-4. Specific gravity 4.

=Malachite.=—Hydrated (basic) copper carbonate. The green copper ore and the common surface alteration product of other copper minerals. Usually has a microscopic structure made up of fine needle-like crystals, but generally massive in various imitative shapes not unlike those of the iron ores. Sometimes earthy. Its color is bright green, and it is usually found in association with other characteristic copper ores, such as chalcopyrite and azurite. When relatively pure and in large masses, it is a beautiful ornamental stone. Effervesces with acid. Hardness 3.5-4. Specific gravity 4.

=Azurite.=—Hydrated (basic) copper carbonate, less hydrated than malachite, and known as the blue carbonate of copper. Generally in very minute and quite complex crystals, but also in imitative shapes similar to those of malachite, and at other times earthy. Slightly lighter in weight than malachite, from which it is easily distinguished, as from most other minerals, by its bright azure blue color and its somewhat lighter blue streak. Effervesces with nitric acid. Hardness 3.5-4. Specific gravity 3.7-3.8.

=Calcite.=—Calcium carbonate, CaCO_{3}. Almost always in crystals (Fig. 486, ^{10-13}), or in confused crystal aggregates, though rarely fibrous or dull and earthy. Some of the forms of the crystals are described as “dog-tooth spar”, others as “nail-head spar”, while still others are modified hexagonal prisms. There is a beautifully perfect cleavage of the mineral along three directions which make angles of about 105° with each other, so that under the hammer the substance breaks into blocks which are shaped like the crystal of Fig. 486, ^{10}. Usually white or gray, but occasionally faintly tinted. Streak white. Effervesces with cold and dilute mineral acids. An associate of many ores and the chief mineral of limestone. A similar mineral—dolomite—contains in addition magnesium carbonate, has simpler crystals (like the drawing of Fig. 486, ^{10}, but often with rounded faces), and effervesces only when the acid is warmed. Hardness 3. Specific gravity 2.7.

=Gypsum.=—Hydrated calcium sulphate, CaSO_{4}.2 H_{2}O, and the source of plaster of Paris. Often in simple crystals (Fig. 487, ^1) or else “swallow tail”, like Fig. 487, ^2; in which case the mineral is generally either transparent or translucent and is described as selenite. Such crystals show a cleavage approaching in perfection that of the micas, but, unlike the mica laminæ, those produced by cleavage in gypsum though flexible are not elastic. There are also fibrous forms of gypsum (satin spar), a fine-grained form (alabaster), and the impure earthy form (rock gypsum). Very soft, light in weight, and difficultly fusible. Color usually white, gray, or pale yellow. Hardness 2. Specific gravity 2.3.

=Copper glance.=—A sulphide of copper, Cu_{2}S. Not usually well crystallized, but generally massive and associated or variously admixed with other copper ores such as chalcopyrite, malachite, etc. Fracture conchoidal, luster metallic, color and streak blackish lead-gray, though often tarnished blue or green from surface alterations to the copper carbonates. Softer and heavier than chalcopyrite. Blowpipe or chemical tests are necessary for its identification. Hardness 2.5-3. Specific gravity 5.5-5.8.

=Cerussite.=—The white or carbonate lead ore, PbCO_{3}, and an important ore of silver as well. Often in crystals of considerable complexity, though Fig. 487, ^{3-4}, shows some common shapes. Often granular, massive, or earthy (gray carbonate ore). Very brittle and with conchoidal fracture. The luster is adamantine or like that of oiled glass. Color generally white or gray. Very heavy, the heaviest of light colored and nonmetallic minerals. Dissolves in nitric acid with effervescence. Hardness 3-3.5. Specific gravity 6.5.

=Siderite.=—The carbonate or “spathic” ore of iron, FeCO_{3}. Either in crystals resembling in form Fig. 486, ^{10}, but with rounded faces, or cleavable massive to finely granular and earthy. The crystalline varieties cleave easily into smaller blocks of the same form as those of calcite. Color usually gray or brown and streak white. On strongly igniting, the white powder becomes black and magnetic. Lighter in both color and weight than the other iron ores, and unlike them siderite effervesces with acid. Distinguished from calcite by its higher specific gravity and its change upon being ignited. Hardness 3.5-4. Specific gravity 3.9.

=Smithsonite.=—Carbonate of zinc, ZnCO_{3}, and an important ore of that metal. Seldom found in crystals except as a replacement of calcite crystals, in which case it shows the forms characteristic of the latter mineral. Usually kidney-shaped, stalactitic, or else in incrustations upon other minerals. Sometimes granular or earthy. Brittle. Luster vitreous, color white or greenish gray, though often stained yellow with iron rust. Streak white except when the mineral is stained with iron. Effervesces with warm acid. Hardness 5. Specific gravity 4.4.

=Pyrolusite.=—Black oxide of manganese, MnO_{2}, though generally impure from admixture with other manganese oxides. Usually in intricate aggregates which may be columnar, fibrous, mammillary, earthy, etc. Opaque, with color and streak both black. Soft and easily soils the fingers. With hydrochloric acid gives off the choking fumes of chlorine. Hardness 2-2.5. Specific gravity 4.8.

II. The Minerals important as Rock Makers

These minerals are in most cases complex silicates of one or more of a certain number of metals such as aluminium, calcium, magnesium, iron, sodium, potassium, or hydroxyl (OH). For their identification an examination of the physical properties is usually sufficient, whereas of the typical ore minerals already considered, additional chemical tests may be necessary.

=Feldspars.=—A group of similar alumino-silicates of potassium, sodium, and calcium. The most important of all rock-making minerals. Although with wide variation in chemical composition, the feldspars are yet broadly divided into two classes; the one striated, and the other an unstriated potash or orthoclase variety. The pocket lens is usually necessary in order to make out the striations upon the crystal or cleavage surfaces. When formed in veins, feldspar appears in crystals (Fig. 487, ^{5-6}), but as a rock constituent the mutual interference of crystals prevents the development of bounding faces. Two cleavage directions, nearly or quite perpendicular to each other, are notably different in their perfection. Hard enough to scratch glass, but easily scratched by sand. Color pink (usually orthoclase or microline), white (often albite) to gray. Sometimes with beautiful “pigeon’s throat” effect of iridescence (labradorite). Low specific gravity. Hardness 6. Specific gravity 2.5-2.8.

=Quartz.=—Oxide of silicon or silica, SiO_{2}. Both an important vein mineral associated with the ores and a rock maker. In the former case particularly, often in crystals of notably simple forms (Fig. 487, ^7). Few minerals which are not gems are so hard. Remarkable freedom from cleavage so that the mineral breaks much like window glass—conchoidal fracture. Wide range in both transparency and color. Transparent and colorless crystalline variety (rock crystal), brown translucent (smoky quartz), turbid white (milky quartz), and various colored varieties (carnelian, jasper, jet, etc.). Insoluble in acids and infusible. Hardness 7. Specific gravity 2.6.

=Micas.=—Like the feldspars a group of complex silicates, but here chiefly of potassium, magnesium, iron, and hydroxyl. Abundant as rock makers, the micas are all characterized by the thinnest and toughest of elastic cleavage plates, such as are generally known as isinglass. When a needle is driven sharply through a thin scale of mica, a six-rayed puncture star forms about the needle point. The darker common variety of mica is rich in iron and magnesium and is called biotite, and the lighter colored alkaline variety, muscovite. Hardness 2.5-3.1. Specific gravity 2.7-3.1.

=Chlorite.=—Generally an intricate mixture of more or less similar microscopic crystals having varying and rather complex chemical compositions and related to the micas, but all characterized by a peculiar leaf green color. These minerals are a common product of hydration weathering in rocks which are rich in magnesium and iron—especially those that contain biotite, pyroxene, or hornblende (see below). Hardness 1-2.5. Specific gravity 2.5-3.

=Pyroxenes.=—An important group of related rock-making minerals all of which are silicates of the bases magnesium, calcium, aluminium, iron, and manganese. Quite generally developed either in columnar or needle-like crystals which are uniformly shaped in cross section like Fig. 487, ^8. Two rather imperfect cleavages are directed parallel to the longer axis of the crystal and nearly at right angles to each other. The colors of all but the lime varieties are dark and generally green, dark brown, bronze, or black. The lime varieties are white, gray, or pale green. A dark colored and common iron variety is known as augite. Streak generally either white or lightly tinted. Hardness 5-6. Specific gravity 3.2-3.6.

=Amphiboles.=—A group of minerals of the same chemical composition as the pyroxenes, with which also in most physical properties they agree. The principal distinction is found in the shape of the cross section and in the cleavage (Fig. 487, ^9). Whereas the cross sections of pyroxenes are generally eight sided, those of the amphiboles have six sides, and whereas the cleavage directions of pyroxenes are nearly at right angles to each other (87°), the similar but much more perfect cleavage directions of the amphiboles are inclined at an obtuse angle (124½°). Owing to the obliquity of the amphibole cleavage, fractured surfaces of the mineral appear splintery, which is not in the same measure true of the pyroxenes. A fibrous variety of amphibole, and occasionally other varieties of the mineral, is a not uncommon product of weathering of pyroxenes. Other physical properties of the amphiboles are in the main almost identical with those of the pyroxenes.

=Garnet.=—Complex alumino-silicates or ferro-silicates of calcium, magnesium, iron, or manganese, or several of these combined. Nearly always in crystals, and usually found in mica schist (see below). The crystals usually have twelve similar faces, each a lozenge (dodecahedron), or else twenty-four similar faces, or the two forms combined (Fig. 487, ^{10}). Brittle. From any but the gem minerals garnet is easily distinguished by its hardness, which in different varieties ranges from somewhat below to somewhat above that of quartz. The luster is vitreous, and the color runs the gamut of reds, browns, and greens, but with the common hue dark red to black. Streak white. Hardness 6.5-7.5. Specific gravity 3.1-4.3.

=Nephelite= (=nephelene=).—An alumino-silicate of sodium and potassium. In certain special provinces this mineral is developed in abundance as an essential constituent of igneous rocks, but elsewhere practically unknown. The rare crystals are hexagonal prisms (Fig. 487, ^{11}), but the mineral is most easily determined by its general resemblance to feldspar, but with the differences of cleavage, luster, and reaction with acid. Whereas the feldspars have two cleavages, either nearly or quite perpendicular to each other and of different degrees of perfection, nephelite has three equal cleavages inclined 60° and 120° to each other and of less perfection than either feldspar cleavage. The luster of nephelite is perhaps the best clew to its identity, since this is greasy and simulated by but few minerals. The fine powder of the mineral treated for some time with strong hydrochloric acid forms a perfect jelly of silicic acid, whereas the feldspars do not. Though itself gray or white and unobtrusive, nephelite is usually associated with brightly colored minerals, which are often the first clew to its presence in a rock. Hardness 5.5-6. Specific gravity 2.5-2.6.

=Talc= (=soapstone=).—A silicate of magnesium and hydroxyl which is an important alteration product through weathering of certain pyroxene rocks especially. Usually a foliated mass, this product is occasionally fibrous or even granular. Talc is one of the softest of minerals, having a greasy feel and being easily scratched with the thumb nail. The luster of the foliated varieties is apt to be pearly, and the color apple-green to white, though sometimes stained brown from oxide of iron. The streak of the mineral is white except when stained by iron. Although the rocks which are composed mainly of talc (soapstone) are exceedingly soft, they are very tough and remarkably resistant. Hardness 1-1.5. Specific gravity 2.7-2.8.

=Serpentine.=—Like talc, serpentine is a silicate of magnesium and hydroxyl, and an important product of the breaking down of magnesium minerals in the process of weathering. The mineral is usually found as a fine web of microscopic needle-like fibers, and is best roughly diagnosed by its color and its associated minerals. Like talc it is usually developed within those igneous rocks from which feldspar is lacking, but where either pyroxene or olivine is found in abundance or was previous to alteration. The characteristic color of serpentine is leek-green. The rock largely composed of serpentine is called by the same name, and being exceedingly tough and unchanging is, in spite of its softness, a valuable building and ornamental stone. A red magnesium garnet is apt to be associated with such serpentine masses. Hardness 2.5-4, because of impurities. Specific gravity 2.5-2.6.

=Staurolite.=—A silicate of aluminium, iron, and hydroxyl. Found in metamorphic rocks usually in association with garnet. Always in crystals bounded by simple forms generally crossed, as shown in Fig. 487, ^{12-14}. The color is dark reddish brown, and the streak is colorless to grayish. The hardness is exceptional and higher than that of quartz. Hardness 7-7.5. Specific gravity 3.6-3.7.

=Tourmaline.=—An exceptionally complex silicate of boron and aluminium as well as iron, magnesium, and the alkalies. Found in metamorphic rocks and always crystallized. The crystals are columns or needles whose cross section is the best guide to their identity, since this is a modified triangle unlike that of any other mineral (Fig. 487, ^{15-16}). Additional diagnostic properties are the characteristic striations which run lengthwise of the crystals upon prism faces, and the lack of any cleavage (difference from hornblende). The hardness is also a valuable property, since this is greater than that of quartz. The mineral is brittle and the fracture subconchoidal. The range in color is as great as, or greater than, that of garnet, though the common forms are jet black. Streak uncolored. Hardness 7-7.5. Specific gravity 3-3.2.

=Olivine.=—A silicate of magnesium and iron and a rock-making mineral found only in those igneous rocks which have little or no feldspar. It easily suffers alteration by weathering and passes into serpentine, and in fact is seldom found except when at least partially altered to the fibrous webs of that mineral. The form of the unaltered crystals within the rocks is shown in Fig. 487, ^{17}, and, cut in sections, the mineral appears in more or less elongated hexagons. The hardness of the unaltered mineral is about that of quartz. It has rather imperfect cleavages in two rectangular directions, and is usually translucent, with a vitreous luster and a color which is olive-green when not stained brown by oxide of iron. Streak uncolored. Hardness 6.5-7. Specific gravity 3.2-3.3.

APPENDIX B

SHORT DESCRIPTIONS OF SOME COMMON ROCKS

In Chapter IV the classification and the structure of rocks have been briefly discussed. Below are added brief descriptions of the more important common rocks. For rocks as for minerals it is, however, essential that a collection of well-chosen specimens be studied for purposes of comparison. A small pocket lens is a valuable aid in making out the component minerals and the textures of the finer grained rocks.

1. Intrusive Rocks

=Granite.=—Of granitic texture, though sometimes porphyritic as well. The most abundant mineral constituent is a pink or white feldspar, usually without visible striations, with which there is usually in subordinate quantity a white striated feldspar. Next in importance to the feldspar is quartz, which because of its lack of cleavage shows a peculiar gray surface resembling wet sugar. In addition to feldspar and quartz there is generally, though not universally, a dark colored mineral, either mica or hornblende. The mica is usually biotite, though often associated with muscovite.

=Syenite.=—Like granite, but without quartz, with more striated feldspar, and generally also the rock has a darker average tint. While biotite is the commonest dark colored constituent of granite, hornblende is more apt to take its place in syenite. Less common than granite, to which it is closely related in origin and in composition.

=Gabbro.=—A dark colored rock of granitic texture composed of striated feldspar with broad cleavage surfaces and usually an abundance of pyroxene. In contrast to the feldspars of granite, those of gabbroes are often dull and colored grayish yellow or greenish. The pyroxene is often in part changed to fibrous amphibole. Magnetite may be an abundant accessory mineral.

=Diabase.=—In color dark like gabbro, and of similar constitution. In diabase, however, the feldspar crystals, instead of being broad and of irregularly interrupted outline, are relatively long (“lath-shaped”), and the pyroxene acts as a filler of the residual space between them.

=Peridotite.=—A heavy and dark colored rock of granitic texture which is nearly or quite devoid of feldspar but contains olivine. When altered, as it generally is, it is largely a mass of serpentine, talc, and chlorite, surrounding cores, it may be, of still unaltered pyroxene and olivine. Magnetite is an abundant constituent, and a red garnet is apt to be present.

2. Extrusive Rocks

=Obsidian.=—A rock glass rich in silica. It is usually black and breaks with a perfect conchoidal fracture. It often passes over through insensible gradations into pumice, which differs only in its vesicular structure. As regards chemical composition, obsidian and pumice are not notably different from rhyolite (below).

=Rhyolite.=—A light colored rock of porphyritic texture, often also with fluxion or spherulitic textures, or both combined. The porphyritic appearance is given the rock by large crystals of a glassy, unstriated feldspar and crystals of quartz. Rhyolite is a very siliceous lava containing rather more silica than granite, to which of the intrusive rocks it is most closely related, and from which it differs in its texture and in the manner of its occurrence in nature. Whereas granite is found in great batholites, laccolites, and bysmalites, and consolidated in most cases beneath the earth’s surface, rhyolite generally occurs in sheets, flows, or dikes, and consolidated either above or in fissures near to the surface.

=Trachyte.=—Similar to rhyolite, but usually with a peculiar gray aspect from the greater abundance of feldspar crystals. The rock is less siliceous than rhyolite, contains no quartz crystals, and approaches a feldspar in its average composition.

=Andesite.=—Similar to rhyolite in appearance and in origin, but more basic and correspondingly dark in color. The porphyritic crystals are of lath-shaped, striated feldspar, with which are associated crystals of either biotite or hornblende or both. A fluxion texture is particularly characteristic of this type of extrusive rock.

=Basalt.=—A dark colored or black basic rock of porphyritic texture which differs but little from diabase. It may show under the lens fine lath-shaped crystals of striated feldspar associated with crystals of augite, but more frequently the rock is dense and without visible mineral constituents. It is particularly likely to occur divided up into columns six inches to a foot in diameter and known as basaltic columns. Especially fine examples are known from the Giant’s Causeway and other localities in the western British Isles.

3. Sedimentary Rocks of Mechanical Origin

=Conglomerate= (“=pudding stone=”).—A rock made up from pebbles which are cemented together with sand and finer materials. The pebbles are usually worn by work of the waves upon a shore, and may vary in size from a pea to large bowlders. They may consist of almost any hard mineral or rock, though the sand about them is largely quartz.

=Sandstone.=—A rock composed of sand cemented together either by calcareous, siliceous, or ferruginous materials. Sandstones are described as friable when their surface grains are easily rubbed off, or as compact when they are more firmly cemented. Sandstones are often distinctly banded and are sometimes variously stained with oxide of iron. Those sandstones which have been formed upon a seacoast are known as marine sandstones, while those derived from accumulations collected by the wind in deserts are distinguished as continental deposits. Sandstones form much thicker formations than conglomerates, the latter usually constituting a basal layer only of the sandstone formation (basal conglomerate).

=Shale.=—A consolidated mud stone which is probably the most abundant rock formation. In large part clay admixed in varying proportions with extremely fine sandy grains.

4. Sedimentary Rocks of Chemical Precipitation

=Calcareous tufa= (=travertine=).—Not to be confused with tuff, which is a fragmental extrusive or volcanic rock. Calcareous tufa is formed when waters which contain carbonic acid gas and lime carbonate in solution, give off the gas and with it the power to hold the lime in solution. Such a liberation of the gas may occur when the stream is dashed into spray above a cascade, and the lime is then deposited about the site of the falls. Travertine is generally porous and formed of more or less concentric layers or incrustations. A remarkable illustration is furnished by the travertine deposits of Tivoli and other localities near Rome, since here the material supplies a valuable building stone.

=Oölitic limestone= (=oolite=).—This rock is made up of spherical nodules and so has the appearance of fish roe. Broken apart, each grain reveals in its center a core of siliceous sand about which carbonate of lime has been deposited in concentric layers. It is thought that waters charged with carbonate of lime, in issuing from a river near a sea beach, coat the sand grains of the latter with successive thin films of lime carbonate due to the rhythmic ebb and flow of the tides, evaporation of the adhering water taking place when the sands are exposed at low tide.

5. Sedimentary Rocks of Organic Origin

=Limestone.=—A generally white or gray rock composed of carbonate of lime with varying proportions of clay, silica, and other impurities. The lime carbonate is usually derived from the hard parts of marine organisms, and the argillaceous and siliceous impurities from the finer land-derived sediments which descend with them to the bottom.

=Dolomite= (=dolomitic or magnesium limestone=).—Differs from limestone in containing varying proportions of the mineral dolomite (_ante_, p. 455), which is made up of equal parts of calcium and magnesium carbonates. Difficult to distinguish from limestone unless a chemical test is made for magnesium, though it may be said in general that dolomite is less soluble in cold mineral acids.

=Peat.=—An accumulation of decomposed vegetable matter within small lakes and in lagoons separated from larger ones (_ante_, p. 429). Peat represents the first stage in the formation of coal from vegetable matter, and differs from the coals by its larger proportion of contained water. Because of this water its fuel value is correspondingly small. It is usually dark brown or black and reveals something of the structure of the plants out of which it was formed.

6. Metamorphic Rocks

=Gneiss.=—A generally more or less banded (gneissic) metamorphic rock with a mineral constitution similar to granite, and often developed by metamorphic processes from that rock. It may at other times, by processes not essentially different, be derived from sedimentary formations. It usually contains as important constituents unstriated feldspar and quartz, but in addition it may include a striated feldspar, biotite, muscovite, or hornblende, or several of these combined. In proportion as mica or hornblende is abundant, it has a marked banded texture, but it differs from mica schist (see below) not only in the presence of its feldspar, but in the smaller proportion of mica. Biotite gneiss, hornblende gneiss, etc., are terms used to designate varieties in which one or the other of the dark colored constituents predominate.

=Mica schist.=—A metamorphic rock without feldspar and mainly composed of quartz and light colored mica (muscovite). The abundant mica lends to the rock its characteristic schistose texture, which differs from the usual gneissic texture. In some cases the mica is wrapped about the grains of quartz, but at other times it forms a series of almost continuous membranes separating layers of quartz.

=Sericite schist.=—A variety of schist which is characterized by an abundance of a peculiar silvery mica rich in the element group hydroxyl. The mica scales are often microscopic and wrought into an intricate web with the quartz constituent.

=Talc schist.=—A schist made up largely of talc, but with varying proportions of quartz, magnetite, etc. From the abundance of the talc it is usually pale green or white.

=Chlorite schist.=—A greenish, fine-grained metamorphic rock in which chlorite is the principal mineral, but in which magnetite is a quite characteristic accessory constituent.

=Staurolitic garnetiferous mica schist.=—A mica schist in which garnet and staurolite are so abundant as to be essential constituents.

=Clay slate.=—A metamorphosed mud stone or shale. In the process of metamorphism the rock has been hardened, given a slaty cleavage, and innumerable minute scales of mica have developed to produce a silky luster upon the cleavage faces. The color may be gray, green, purple, or black.

=Quartzite.=—A metamorphosed sandstone in which the sand grains have become enlarged by accretion of silica. Whereas a sandstone fractures about its constituent grains, a break in quartzite is continued through the grains and the cement alike. In contrast to sandstones, the quartzites derived from them are usually lighter in color and often nearly white.

=Marble= (=crystalline limestone=).—The result of metamorphism upon limestones. Usually white in color but sometimes gray, blue gray, or yellow, and sometimes variously broken or brecciated and stained with iron oxide. Effervesces with cold dilute acid.

=Coals.=—Under the head of peat the first stage in the formation of coals from vegetable matter has been briefly described. Lignite, or brown coal, represents a further stage and one in which the vegetable structure is still recognizable. It is usually brownish black or black in color and contains a considerable proportion of water. With increased pressure or dynamic metamorphism, further percentages of the volatile constituents are eliminated, and when from seventy-five to ninety per cent of carbon remains, the material burns with a yellow flame and is known as bituminous coal. This is the great fuel for the production of steam. A continuation of the metamorphic processes carries off a further proportion of the volatile matter and leaves a dense, hard, black substance with sometimes as much as ninety-five per cent of carbon. This is the so-called “hard coal” or anthracite generally used for fuel in our houses, for which purpose it is so well adapted because it burns with a production of much heat and almost without smoke.

APPENDIX C

THE PREPARATION OF TOPOGRAPHICAL MAPS

=Topographical maps a library of physiography.=—For the satisfactory working out in detail of the geology of any region of complex structure, an accurate topographical map is prerequisite. This is so much the more true because nearly all complexly folded or faulted rock masses are to be found in mountainous, or at least in hilly regions. The making of the topographical map must, therefore, precede that of the geological map, and in modern usage the latter is a topographical and a geological map combined in one.

Within certain narrow limits, predictions concerning the geological history of a province may often be made by an expert geologist from examination of an accurate topographical map. Just as in forecasting the weather upon the basis of the usual weather maps, such predictions can sometimes be made with entire confidence in their accuracy, while at other times a guess only may be hazarded. The great value of the modern topographical map is becoming, however, universally acknowledged, and every highly civilized nation has either completed or has in preparation sectional topographical maps of its domain on such a scale as is warranted by its financial condition and its state of development. Thus there is now being accumulated a vast library of geographical and to some extent geological information, of which the student of geology must be prepared to make use.

=The nature of a contour map.=—More and more the contour map is replacing the earlier and less scientific methods of representing topography on the large scale sectional maps, and hence this type only need here be considered. In the contour map, the relief of the land is represented by a series of curving lines, each the intersection of a particular horizontal plane with the land surface, and the several planes separated by uniform differences of elevation. This altitude interval is known as the contour interval. Its choice is a matter of considerable importance, for though regions of relatively simple topography may be adequately represented upon a map of large contour interval, say one hundred feet, another district may require an interval as short as five feet. A contour map with this interval may be conceived to have been made by flooding the region which it represents and preparing maps of the shore lines for each rise of five feet of the water surface, and superimposing the several maps thus derived with accurate registration one above the other. Wherever the land slopes are steep, the shore lines of the several maps will be crowded closely together and give the effect of a relatively dark local shade; where, upon the other hand, the surface is relatively flat, the several shores will be widely spaced and the effect will be to produce a white area upon the map. Thus in contour maps dark tones indicate steep gradients and pale tones a flatness of surface.

=The selection of scale and contour interval.=—With the use of the small scale in the contour map, the tones of the map will be correspondingly dark, though the relative differences in tone will remain the same. With the use of a closer contour interval the tones will deepen throughout. The adjustment of scale and contour interval to any given region is a matter requiring experience in topographical mapping, and in addition a knowledge of the geological significance of topographic features. Unfortunately, the element of expense and the special commercial objects held in view, conspire to select scales and contour intervals which are often little adapted to the districts surveyed.

=The method of preparing a topographical map.=—Having fixed upon the scale and the contour interval which is to be employed, the task of the topographical surveyor is next to fix accurately the positions and the elevations of a sufficient number of points to _control_ the map, and then to hang, as it were, upon these points as attachments the design represented by the relief. Were the surface of the ground to be represented by a flexible fabric, the map maker might raise from a flat base a series of stout posts of the heights and in the positions which he has determined, and upon these supports arrange the slopes of the fabric much as drapery is adjusted. The determination of the exact positions and the elevations of his control stations is, therefore, a process coldly precise and formal; whereas in the shaping of the surfaces his attention should be fixed more upon correctly reproducing the shapes than upon fixing accurately the position of every point. As a matter of fact, the position of the average point will be most accurately fixed when the shapes of the features are most clearly comprehended. To some extent, therefore, the topographer should be familiar with the geological significance of the earth features which he is representing.

=Laboratory exercises in the preparation of topographical maps.=—The principles which underlie the surveyor’s method for preparing a topographical map may be learned in the laboratory by the use of models and the simple device shown in plate 24 A and B. To represent the section of country to be mapped a model in plaster of Paris is substituted, and this is placed within a rectangular tank to which locating carriages and altitude gauges are attached that allow the student to fix the position and the elevation of any point upon the surface of the model.

┌──────────────────────────────────────────────────────────────────┐ │ PLATE 24. │ │ │ │ [Illustration: _A._ Apparatus for exercise in the preparation of │ │ topographic maps.] │ │ │ │ [Illustration: _B._ The same apparatus in use for testing the │ │ contours of a map.] │ │ │ │ [Illustration: _C._ Modeling apparatus in use.] │ └──────────────────────────────────────────────────────────────────┘

Upon each model the student “locates”, or fixes, the position of a sufficient number of points for the control of his map, entering upon an appropriate map base for each position the altitude which was read from the gauges. Now _with the map always before him_ he “sketches in” the forms of the surface by means of contour lines. For this purpose it is often desirable to fix roughly the direction of the steepest slope at a number of places, and noting the differences in elevation between control stations, divide up the distance in accordance with the curves of slope and start the contours at right angles to the slope. Afterwards such sections are connected by sketching in with the model always in view for control (Fig. 488).

=The verification of the map.=—The map prepared, its accuracy may be tested by a simple method which is denied the topographer who has to do with the actual surface of the ground. The locating carriages and altitude gauges are removed from the tank, which is next filled with water and leveled by means of guide marks upon the interior. A few drops of milk or of ordinary clothes blueing are added to the water to render it opaque, and it is then drawn off at the faucet in successive installments, so that the surface drops by layers corresponding in thickness to the contour interval of the map, plate 24 B. As each layer is withdrawn, that contour of the map to which the shore line should correspond is carefully examined and corrected. By such corrections the nature of the first errors made is soon appreciated, and the method of procedure is thus more easily acquired. At the same time the significance of the design of the map is more quickly learned than by a mere examination of the standard government maps.

The work above outlined calls for waterproofed models of suitable form and size, and a series, each of which sets forth some typical feature or series of features, has been designed by Mr. Irving D. Scott.[2]

=The preparation of physiographic models.=—The apparatus used to prepare the topographic map is adapted also for preparing a physiographic model from a standard topographical map. For this purpose the method is essentially reversed, though the tank is replaced to advantage by a light metal frame elevated upon one side so as to permit a free use of the hands in modeling the clay.

The material used in preparing the model is artists’ modeling clay[3] which has a base of beef suet, and hence does not dry out and crack as does ordinary clay. Its form is, therefore, retained indefinitely, and it may be used again and again. Most maps must be enlarged in modeling, and the simplest way is often to photographically or by pantograph enlarge the map to the scale of the model. The map prepared, it is covered by a thin celluloid plate which has cut upon it a series of crossed lines spaced in inches and larger subdivisions to correspond to those of the locating carriages (plate 24 C).

The enlargement of the map is not essential to experienced workers, and the standard map may be covered in similar manner by a transparent plate with “checkerboard” design, the squares of which bear some simple relation in size to the larger divisions of the locating carriages (Plate 24 C, rear).

The method of preparing the model is comparatively simple. Beginning at any point upon the map, the intersection of a heavy contour line with one of the guide lines of the celluloid “position plate” is carefully noted. Both the position and the elevation of this point are fixed by the point of the altitude gauge of the modeling frame, and the clay built up beneath it to that height. With the fingers the clay is now roughly shaped in various directions from this point, the altitude gauge is advanced by the locating carriage so as to correspond in position to the intersection of the next heavy contour line with the same guide line of the position plate, and the elevation for this point similarly adjusted upon the model. As before, the surface of the clay is roughly shaped in advance and upon the sides so as to conform to the indications of the map; and this process is repeated until the work is finished. Corrections for intermediate positions may be carried to any desired degree of refinement which the scale and the accuracy of the map permit. Models which are larger than the area of the modeling frame are prepared by making a square foot at a time by the above described process, and then moving the frame forward and adjusting in a new position by means of the sharp pins in the legs of the apparatus.

READING REFERENCES

WILLIAM H. HOBBS, New Laboratory Methods for Instruction in Geography, Journal of Geography, vol. 7, 1909, pp. 97-104. Also Scot. Geogr. Mag., vol. 24, 1908, pp. 643-652. The Modeling of Physiographic Forms in the Laboratory, _ibid._, vol. 8, 1910, pp. 225-228.

APPENDIX D

LABORATORY MODELS FOR STUDY IN THE INTERPRETATION OF GEOLOGICAL MAPS

The laboratory models which have been described on page 63, and are used to represent outcrops in the study of geological maps, are shown in Fig. 489. The drum-shaped blocks serve to represent massive rocks which occur in irregularly shaped masses such as batholites and flows. The long, narrow strips are for intrusive rocks in the form of dikes, while the larger blocks provided with a swivel joint are used for outcrops of sedimentary rocks, and after adjustment they give the dip and strike of the exposure. The wing bolts used in their construction should be of bronze, because of the effect of iron upon the compass. For the same reason tables should not be placed near iron beams or columns. All these blocks can be made by an ordinary carpenter, and should be available in sufficient numbers to arrange problems like those of Figs. 47, 48, and 490. With a view to supplying suggestions for other problems of the same general nature, the three additional field maps of Fig. 491 have been introduced.

The list of questions given below is intended to indicate the nature of some of the problems which the student should be asked to solve in the preparation of each map. The numbers in parentheses refer to pages in this book where further information is given:—

STRATIGRAPHICAL

1. Of the formations represented what ones are sedimentary and what igneous (Chap. IV, App. B)?

2. Which formations, if any, are separated by unconformities (51-53)?

3. What is the order of age of the sedimentary formations (65)?

4. What are the _exposed_ thicknesses of each of these formations (48-49)?

5. Do any of these values represent full thickness of the formation, and if so, which ones?

6. What is the age in terms of the sedimentary formations of each of the igneous rock masses (65)?

7. Which igneous rocks, if any, occur in batholites (143, 441)? Which, if any, in dikes (140)?

STRUCTURAL

8. What formations, if any, have monoclinal dip (42)?

9. Indicate upon the map by dashed lines the crests of all anticlines and the trough lines of synclines.

10. Indicate by arrows the direction of pitch of all plunging anticlines and synclines wherever disclosed by changes of dip and strike (43).

11. Indicate the approximate position of all faults whose position is disclosed (58-61), and, if possible, state which limb is the one downthrown.

12. Prepare suitable geological sections.

READING REFERENCE

WILLIAM H. HOBBS. Apparatus for Instruction in Geography and Structural Geology. III. The Interpretation of Geologic Maps. School Science and Mathematics, vol. 9, 1909, pp. 644-653.

APPENDIX E

SUGGESTED ITINERARIES FOR PILGRIMAGES TO STUDY EARTH FEATURES

The chief value of the laboratory studies discussed in the preceding appendices is as a preparation for observations made in the field—the laboratory _par excellence_ of the geologist. The pilgrimages whose itineraries are here suggested have been planned especially for impressing by observation the lessons of this book. Such journeys are best interrupted at a relatively small number of localities which, because already studied in some detail, are specially adapted to serve as centers for local excursions. These localities will in most cases be the great scenic places to which tourists resort, or the seats of universities near which specially detailed explorations have been often made.

Within the United States a few local geological guides have been published, and the Geologic Folios published by the United States Geological Survey are already available for a number of such centers. For one long geological pilgrimage we are fortunate in having a carefully prepared guide, namely, from New York to the Yellowstone National Park and back, with a side trip to the Grand Cañon of the Colorado. Except for the side trip this route, in large measure, corresponds with one here chosen, and for the return journey especially the student is referred to it for information (Geological Guide Book of the Rocky Mountain Excursion, edited by Samuel Franklin Emmons. Comte Rendu de la Congrés Géologique Internationale, 5me Session, Washington, 1891, 1893, pp. 253-487, map and plates 13, figs. 32).

Our journey is begun at New York City, which is built about the deeply submerged channels of an estuary choked with glacial deposits, though the channel may be followed as a deep cañon across the continental shelf to its margin (252,[4] pl. 17 B). New York City is also upon the margin of the glaciated area, the outer terminal moraine of which is well represented on Long Island (298). Across the Hudson in New Jersey is the great Coastal Plain which meets the oldland in a well-defined margin (159, 246, 247). A local geological guide of the vicinity of the metropolis has been written by Gratacap (Geology of the City of New York, Greater New York. Brentanos, New York, 1904, pp. 119, pls. and map).

Traveling by the New York Central Railway, we follow up the Mohawk outlet of the glacial lakes Iroquois and Algonquin (334), first skirting upon the east the great sills of intrusive basalt known as the Palisades, with their markedly columnar jointing and intersections by numerous faults. Above Peekskill we enter the picturesque narrows of the river (174), cut in the hard crystalline rocks of the Highlands. Entering the Mohawk Valley, we pass Syracuse with limestone caverns and well-oriented joints widened by solution through the agency of the descending ground water (181, pl. 6 B). A branch line to the southwest reaches the vicinity of Cayuga Lake and Ithaca, where are well-oriented joints which have controlled the drainage directions, and there is also a typical strath (55, 87, 428).

To Niagara Falls at least a day should be allotted for the “gorge ride” by trolley car, thus making the complete circuit of the brink of the gorge with interruptions and local studies at all important points (352-366, pl. 23 A). From Niagara Falls over the Michigan Central Railway we reach Detroit on the present outlet of the upper Great Lakes as well as of the later Lake Algonquin (334). From this city as a center a trip is made by electric railway to Ypsilanti and Ann Arbor, across the bottoms of the early glacial lakes from the first Maumee to Warren (330-333). The strong Whittlesey beach is encountered at the little station of Ridge Road, and one of the Maumee beaches on Summer Street in Ypsilanti. The city of Ypsilanti is built upon a terrace (165) of the Huron River, and another terrace in the same series is crossed by the electric line. In an excursion of a few miles down the river, passing meanders (164-165) and ox-bow lakes (165, 415), is found an interesting case of stream capture near the little village of Rawsonville (175. See Isaiah Bowman, Jour. Geol., Vol. 12, 1904, pp. 326-334).

Continuing our journey from Ypsilanti over a high moraine (312), Ann Arbor is reached, built upon the level plain of outwash with fosses sometimes separating it from the moraine (281, 314). Upon the campus of the university are great bowlders of jasper conglomerate and jaspilite, which were transported from the north by the continental glacier (305). Across the river from the Michigan Central station and behind the little church is a delta formed in one of the glacial lakes Maumee and here opened in section (168). West of the city is a great valley which was the former course of the Huron River when thus diverted by the continental glacier lying to the eastward of Ann Arbor—border drainage (see Ann Arbor folio by the U. S. G. S., and, further, R. C. Allen and I. D. Scott, An Aid to Geological Field Studies in the Vicinity of Ann Arbor, George Wahr, publisher, Ann Arbor).

Returning to Detroit (M. C. Ry.), the great Sibley quarries in limestone near Trenton may be visited. They display perfect jointing, numerous fossils, and especially well-glaciated surfaces interrupted by deep troughs and showing striæ of several glaciations (304). From Detroit the journey is continued by steamer to Mackinac Island in the strait connecting Lakes Michigan and Huron, passing on the way through the peculiar delta of the St. Clair River (431), and coming in view of the notched headlands, which are a monument to the post-glacial uplift of the glaciated area (250, 341). A day is spent at Mackinac Island and St. Ignace in order to study with some care these uplifted strands of the late glacial lakes (341-344). Chicago may now be reached either by steamer or by rail, and in its vicinity we may see the elevated beaches and the ancient outlet of Lake Chicago (331-332, 347, pl. 22 A. See Chicago Folio, U. S. G. S.). By the Chicago and Northwestern Railway the area of recessional moraines and intermediate outwash plains, and later that of the drumlins, are crossed in journeying to Madison, Wisconsin. By examination of the maps on pages 308 and 317 in connection with the larger scale atlas sheets of the United States Geological Survey (Janesville, Evansville, and Madison sheets), this car journey can be made most instructive in gaining familiarity with the characteristic glacial features, and this study is continued to special advantage in excursions about Madison as a center (316-317, 407). This is the more true since at numerous localities in the vicinity of Madison the well-striated glacier pavement is exposed for comparison of the striæ as regards direction with the axes of the several types of glacial features.

An especially instructive excursion may be made by carriage in a single day to the “driftless area” some twelve miles west of the city. Before reaching it we cross in alternation a series of recessional terminal moraines (pl. 17 C) and outwash plains, and near Cross Plains encounter the partially dissected upland with its arborescent drainage and even sky line (298, 300-301, 312-313, pl. 16 A and B). Typical shore formations (233, 241, 242) are studied to advantage about Lake Mendota in a walking trip to and beyond Picnic Point, where are found the best ice ramparts (431-434. See Buckley, Trans. Wis. Acad. Sci., Vol. 13, pp. 141-162, pls. 18).

Our journey is now continued over the Chicago and Northwestern Railway to Devils Lake near Baraboo, where we cross a salient of the driftless area, within which lies Devils Lake, imprisoned in a former valley of the Wisconsin River, since diverted to another course as a result of the glacial invasion (312-313). The valley here is a former narrows in hard quartzite (466), which towers above the lake in unstable chimneys (300), such as the Devils Tower, but such remnants are not found on the other side of the moraine, being there replaced by rounded rock shoulders. Just north of the lake the marginal moraine which blocks the valley is so characteristic as to merit special study (pl. 17 C). Only a few miles northward along the railway from Devils Lake is Ableman, where, exposed in a high cliff, the hard purple quartzite with beautiful ripple marks to reveal its plane of sedimentation (pl. 11 A) dips vertically, and is overlain by horizontally bedded yellow sandstone. The marked angular unconformity which is thus displayed is further made evident by a basal layer of conglomerate (463) in the sandstone (51-53). Here also are deposits of loess along the river, which display their vertical joint surfaces (207). An excellent geological guide to this interesting district and that of the neighboring “Dalles” of the Wisconsin River has been written by Salisbury and Atwood (The Geography of the Region about Devils Lake and the Dalles of the Wisconsin, etc., Bull. 5, Wis. Geol. and Nat. Hist. Surv., 1900, pp. 151, pls. 38, figs. 47).

If we have taken a conveyance at Devils Lake for Ableman, we may continue in the same manner to Kilbourn, where begin the picturesque Dalles of the Wisconsin River—here a young gorge cut in sandstone, because the Wisconsin was diverted from its old valley to border drainage at the edge of the driftless area (300, 321). The side cañons of the river, through their abrupt zigzags, reveal the control of their courses by the joint system (224). In the journey up the rapids by steamer to inspect the Dalles, we observe many beautiful examples of cross bedding in the sandstone (37).

From Kilbourn we continue our journey to Minneapolis over the Chicago, Milwaukee, and St. Paul Railway, and near Camp Douglas are over a peneplain, out of which rise prominent monadnocks (171). At La Crosse the Mississippi River is reached, flowing beneath bluffs of sandstone which are capped by loess (207). The meanderings and the numerous cut-offs of the Mississippi may be observed to the left (415). Lake Pepin is a side-delta lake blocked by the deposits of the Chippewa River (419).

From Minneapolis an excursion is made to Fort Snelling to view the young gorge of the Mississippi, cut by the Falls of St. Anthony for a distance of about eight miles in manner similar to that of the seven miles of Niagara gorge (354), and to compare this narrow gorge with the broad valley of the Warren River which drained Lake Agassiz (327). Somewhat farther up the Warren River are examples of saucer lakes (416).

From Minneapolis the journey may be continued by the Great Northern Railway to Livingston, Montana, thus crossing between the stations of Muscoda and Buffalo the bed of Lake Agassiz and its marginal beaches (325-328. For local geology of Minnesota consult C. W. Hall, Geology of Minnesota, Vol. 1, Minneapolis, 1903).

The Yellowstone Park is entered from Livingston (Livingston Geological Folio, U. S. G. S.) and departure from it made at the relatively new Union Pacific terminal at the southwest margin. The regular trip through the Park includes visits to the several geyser basins (191-194), Obsidian Cliff (33, 463), the Cañon of the Yellowstone, etc. Good climbers can make a side trip from near the Mammoth Hot Springs to the top of Quadrant Mountain, the remnant of a “biscuit cut” upland (372), and there study the nivation process (368, Yellowstone National Park Folio, U. S. G. S.).

The trip from the Park to Salt Lake City, over the Union Pacific Railway, passes through the Red Rock Pass, the former outlet of Lake Bonneville (423), into the desert of the Great Basin (Chaps. XV and XVI). Great Salt Lake is a saline lake or sink with an interesting record of climatic changes (198, 401). The front of the Wasatch Range, in view and easily reached from Salt Lake City, is deeply scored by the horizontal shore terraces of Lake Bonneville (198, 199), and these terraces are extended at every reëntrant by barrier beaches of great perfection. In the Pleistocene period mountain glaciers in part occupied the valleys of this range, though they did not always extend as far as the mountain front. Big Cottonwood Cañon, which realizes this condition, and the neighboring Little Cottonwood Cañon, from whose front its glacier spread into an expanded foot (264), thus show for comparison in a single view the V and the low U sections respectively (172, 376). Here are also alluvial fans (213) and recent faults which intersect them.

From Salt Lake City the return to New York may be made by the Denver and Rio Grande Railway across deserts and through the Royal Gorge, the cañon of the Arkansas River. A full itinerary of the points of geological interest along this route, and continued to Chicago, Washington, and New York, is supplied in much detail in the guide of the geological excursion to the Rocky Mountains above cited. This the traveling geologist should not fail to study. Some references to points along this journey will be found on preceding pages of this book (219-220, High Plains; 170, Allegheny Plateau in West Virginia; 176, water gap of Harper’s Ferry; 176-177, 184-186, side trip up the Shenandoah Valley to Luray Caverns and Snickers Gap; 251, Chesapeake Bay).

Instead of returning directly from Salt Lake City, the traveler, if he has sufficient time at his disposal, may extend his journey southwestward across the Great Basin to Los Angeles. A branch line from this route leaves the Vegas Valley and passes within reach of the famous Death Valley (201) to Tonopah (79) and the Owens Valley (77-78, 92), where are many surface faults dating from the earthquake of 1872 and other less recent disturbances. Returning to the junction point, the route continues across the Colorado and Mohave deserts to Los Angeles. From Los Angeles as a center the exceptionally interesting terraces, caves, and stacks of an uplifted coast are to be seen to best advantage near Pt. Harford (Chap. XIX). The islands of San Clemente and Santa Catalina may also be reached from Los Angeles (239, 248, 249, 250, 256, 257, pls. 5 B, 7 A, 12 A). The return to the East, if made by the Santa Fe Railway, permits of a visit to the Grand Cañon (174, 443) from the station of Williams. From that point eastward the geology of the route is fully covered in Emmons’ Guide to the Rocky Mountain Excursion already cited.

* * * * *

For the benefit of those who are privileged to travel in Europe, and the number increases yearly, a pilgrimage is suggested which may easily be made to correspond with plans laid out on the basis of historical, artistic, and scenic points of interest. The only popular guide of a general nature written for geologists traveling abroad appears to be a brief but valuable little paper by Professor Lane (The Geological Tourist in Europe, Popular Science Monthly, Vol. 33, 1888, pp. 216-229). The publishing house of Gebrüder Bornträger in Berlin is now publishing a quite valuable series of geological guides dealing with special districts and written by well-known authorities (Sammlung Geologischer Führer). Of this series some thirteen numbers have already been issued. Many other valuable local guides of a geological nature are the Livrets Guides of the International Geological and Geographical Congresses, and the similar pamphlets supplied in connection with annual meetings of national or provincial geological societies.

Passengers on steamships sailing from the harbor of New York pass out over a deeply submerged cañon (252) largely filled with glacial deposits, through the Narrows (174), and in sight of Sandy Hook, a modified spit (238, 240). To the left are seen the great morainic accumulations at the border of the glaciated area on Long Island (298). In the course of the trans-Atlantic voyage a much-rounded iceberg may be encountered (291), though this is much more apt to occur upon the northern routes from Quebec, and late in the season. Upon entering the English Channel the land on both coasts rises in steep cliffs, where are found all the common shore features well developed (Chap. XVIII). The German steamships pass in sight of Heligoland, that last remnant of wave erosion (236).

While traveling in Europe, the student should consult a map of the glaciated area (299), and so learn to recognize its peculiarities, and carefully mark its marginal moraine (311) and other strongly marked features.

If the British Isles are visited and the more rugged areas are selected, one may study the cirques and other characteristic features due to the presence of mountain glaciers about Snowdon (Chap. XXVI). More mature stages of the same processes are to be found in the Scottish Highlands and the Inner Hebrides, but especially upon the Island of Skye (Fig. 492). A very valuable aid to excursions in this district is Baddeley’s Scotland (part I, Dulau, London) and Sir Archibald Geikie’s Explanatory Notes to accompany Bartholomew’s Geological Map of Scotland (map and notes in cover, Edinburgh, 1892, pp. 23).

It is from Oban, the “Charing Cross of the Highlands”, that one should start out upon the summer steamers in order to reach both Skye and Staffa, the latter with fine basaltic columns (463), and Fingal’s Cave. In sailing to Skye one passes upon either shore of the narrow fjords many relics left in the dissection of volcanoes (139-143 and Sir A. Geikie, Ancient Volcanoes of Great Britain, Vol. II); also rocky islands and skerries marking submergence (252), and the coast terraces which register a later uplift (250). Skye is a complex of many intrusive and volcanic rocks of such markedly different colors as to appear as tints in the landscape. In the Cuchillin Hills of dark green rises the massive gabbro (462) cut by cirques into the jagged pinnacles of horns and comb ridges (373); while lower down and to the east are rounded domes of rhyolite (463) abraded beneath the glaciers and of a delicate salmon tint. Still lower and to the westward are flat mesas composed of horizontal layers of black basalt under a rich carpeting of the brightest verdure. Eastward across the channel are seen the purplish walls of an ancient sandstone. The jagged gabbro core of the island thus represents a fretted upland (372) and is now the training ground of the Alpinist (Abraham, Rock Climbing in Skye, Longmans, London, 1908), while nestled in one of the bottoms of a U-valley is Loch Coruisk, a typical rock-basin lake (412), its shores of hard rock planed and scored.

From Skye we may go to study the remarkable thrusts (45) on the north shore of Loch Maree, a marked lineament, and one directed at right angles to that on the course of the Caledonian Canal connecting Loch Linne with Loch Ness. This northeast wall of Loch Maree is a strikingly rectilinear fault represented by an escarpment, up which we climb to find at the top the crushed and fluted thrust planes of movement dipping southeastward at a flat angle. Here also are beautiful rock-basin lakes, lying in hollows molded beneath the continental glacier. On our way from Skye we have passed up Loch Carron, a sea loch or fjord (252), and along the strath at its head known as Strathcarron (428).

Returning now to Oban, it is but a short trip by steamer up Loch Linne to Fort William along the striking lineament (226) which continues to Loch Ness and beyond (Fig. 492), and thence by rail to Glen Roy and the neighboring glens of Lochaber (322-325).

From Paris as a starting point, we may visit in a most picturesque region the beautifully preserved craters of extinct volcanoes in the Auvergne of Central France (105, 124, 145), which district is entered from Clermont-Ferrand. Here are found the characteristic puys, steep lava domes of viscous lava (105), which figured largely in the early controversies of geologists concerning the origin of rocks.

The rest of our pilgrimage will be so planned as to enter the noble river Rhine at its mouth (Fig. 493), ascend its course to its birthplace in the snows of Switzerland, and after further exploration of the features of this fretted upland, traverse northern and central Italy so as to make our departure for America by the southern route. Entering then upon this course in the Low Countries, we have first the opportunity of observing the characteristics of a great delta with natural levees artificially strengthened as dikes (165-168). Here also are found dunes of beach material which has been raised by the wind into a great rampart near the shore (209-211). Such a wall of dune sand is well displayed at the bathing resort at Scheveningen near the Hague (421). The flood plain of the Rhine (162-165) may be studied in a journey up the river to the university town of Bonn, from whence a day’s excursion should be devoted to the relics of volcanoes known as the Seven Mountains (H. von Dechen, Geognostischer Führer in das Siebengebirge, Bonn, 1861). As a preparation for this trip and others in the volcanic Eifel higher up the river, a visit should be made to the mineral and rock collections of the Poppelsdorfer Schloss at the University. In the volcanic Eifel are found some of the most interesting of crater lakes (405), the largest being Lake Laach with its somewhat peculiar volcanic ejectamenta and its picturesque abbey (see von Dechen, Geognostischer Führer zu der Vulkanreihe der Vorder-Eifel, etc., Bonn, 1886. Consult also Lane, A Geological Tourist in Europe, _l.c._).

Continuing our course up the river from Bonn, we soon enter the gorge of the Rhine cut in an uplifted peneplain (169, 171, 174). From Coblenz, where the Moselle enters the Rhine, a side trip may be made up this tributary river past Zell with its entrenched meanders (173) to the ancient Roman city of Treves. Above Bingen on the Rhine we leave behind us the narrow gorge and rapid current of the river and continue over the broad floor at the bottom of a rift valley (403), lying between the forest of Odin and the Black Forest on the east and the “Blue Alsatian Mountains” far away to the west. At the margins of this plain are beds of loess with their characteristic joint structures and inclusions (207), and in the higher hills on either hand a wealth of intrusive igneous rocks.

At the entrance of the Neckar River to this broad plain is nestled the picturesque castle and university town of Heidelberg, a convenient center for excursions (Julius Ruska, Geologische Streifzüge in Heidelbergs Umgebung, etc., Nägele, Leipzig, 1908, pp. 208, map). At Strassburg (Schwarzwaldstrasse 12) is located the German Chief Station for Earthquake Study, with a particularly large set of modern seismographs. In the university cabinet is also one of the largest and most representative mineral collections in Europe. For excursions in the neighborhood consult Benecke, Sammlung Geognostische Führer, Vol. 5, Elsass, 1900.

From Strassburg we may go by the Black Forest Railway to the Hegau with its volcanic plugs (140), each surmounted by a picturesque castle. We enter next the broadly extended piedmont apron site, above which Lake Constance still remains as a border lake (399). Outwash aprons (314), moraines (311), and drumlins (317) are each in turn encountered. Still continuing our course up the Rhine from Bregenz, we enter the fretted upland (372) of the Alps, mountains composed of great folds and thrusts about a core of intrusive rock (Rothpletz, Sammlung Geologische Führer, Vol. 10, 1902, Thrusts in the Alps between Lake Constance and the Engadine). Some fourteen miles above Chur we pass the terrace produced by successive landslides (414), known far and wide as the Flimser Bergstürz. The further assent of the cascade stairway of this glacier-carved valley brings us to the Furka Pass, from which point magnificent views of the fretted upland are obtained. At the Känzli, a mile from the hotel, one may view the névé of the Rhone Glacier, which may also be easily visited.

We have now followed a great river from its mouth in the sands of Holland to its source in the snows of the higher Alps. Passing over the divide and descending to Gletsch, we may observe the lower end, or foot, of the Rhone glacier and the crevasses and séracs (391) on the steep descent of this radiating glacier (383, 386). The response which glaciers make to climatic changes is here well illustrated by the recession of the glacier front from near the hotel (its position in the ’50s of the nineteenth century) to its present position about a mile farther up the valley.

The characteristics of a glaciated mountain valley may be further illustrated by climbing to the Grimsel Pass, which is scratched and striated (377, 385), and then descending the valley of the Aar to Meyringen (377). Near the Grimsel Hospice are the characteristic rock basin lakes (412), and upon the Aar Glacier to our left were carried out the epoch-making researches of Louis Agassiz, the founder of the glacial theory for explaining the drift. We encounter some thirteen rock bars (377). Just before reaching Meyringen we pass the last of these, the Gorge of the Aar, cut by the stream through limestone.

Interlaken (419) may be made the center for additional excursions up the Lauterbrunnen Valley, with its prominent albs (376) and its ribbon fall of the Staubbach (378). By the Jungfrau Mountain railway we may now ascend partly in tunnels of the rock to the Ewigeismeer, and look down upon the névé and bergschrunds of the Great Aletsch Glacier (370, see Baltzer, Sammlung Geologische Führer, Vol. 10, Bernese Oberland, 1906). Returning to Interlaken by way of Grindelwald, one may study the foot of a radiating glacier, the Untergrindelwald glacier, with its tunnel and its milky and braided stream.

Crossing now the Alpine foreland to Villeneuve at the upper end of Lake Geneva and upon a well-developed strath (426, 428), we may look out upon the turbid waters extending far from the shore of the lake. Journeying to Geneva by steamer we note the gradual clearing of the water until at the outlet of the lake it is as clear as crystal. A walking trip from Geneva takes us to the Bois de la Bâtie, where the Arve with turbid waters meets this clear stream (427).

The railroad to Chamonix ascends another cascade stairway (376), affords views of complexly folded sedimentary rocks (43), and at Chamonix itself the mer de glace supplies opportunities for the study of moraines (386, 393) and glacial movement (390-392). To experienced Alpinists the summit of Mount Blanc offers a remarkably extended outlook over the fretted upland of the Alps (pl. 18 A). From the station of LeFayet below Chamonix, one may ascend to the Désert de la Platé, where are Schratten in limestone due to solution (188).

Crossing by one of the passes to the valley of the Rhone at Martigny we may reach Zermatt, to-day the climbing center of the Alps. From the subordinate cirques surrounding this village descend the Gorner, Findelen, St. Theodul, and other components of this radiating glacier. A black tooth of rock, the Matterhorn, towers above the other peaks and shows to greatest advantage this feature of glacial sculpture (374), while the Gorge of the Gorner is a severed rock bar like that of the Aar (377). Either on foot or over the mountain railway we may ascend to the Gorner Grat, a subordinate comb ridge (373) which affords one of the most magnificent and instructive views of radiating glaciers.

From Brig, farther up the Rhone Valley, an excursion is made to the Eggishorn Hotel, a center for study on and about the Great Aletsch Glacier (329, 371, 385, 388, 395, 410). The easy ascent of the Eggishorn is rewarded by a view almost directly downward upon the ice-dammed Márjelen Lake (329, 411).

From Brig one may make his entry into Italy, either over the picturesque Simplon route afoot or by diligence, or else beneath it through the railway tunnel. By an alternation of short steamboat and rail trips the journey is continued in a direction transverse to the longer axes of the border lakes Maggiore, Lugano, and Como, and later southward to Milan. In leaving the village of Como we pass over heavy morainic deposits on the apron borders of the expanded-foot glacier (383, 385) which once occupied the valley above. On the journey from Milan to Venice, over the fertile plains of Lombardy, the similar accumulations about Lake Garda (414) are first encountered at the little station of Lonato and left behind at Somma Campagna (Tornquist, Sammlung Geologische Führer, Vol. 9, Northern Italy, 1902).

The city of Venice is built upon pile foundations in the lagoon behind the barrier beach known as the Lido (242, 428-429). From here we may reach the Karst country by way of Trieste, some of the more interesting and typical features being found near Divača (187-189, 422, pl. 6 A). In a different direction from Venice by way of Belluno we enter the Dolomites with their patterned relief and battlemented towers (228, 445).

Additional centers for geological excursions on the route to our point of departure from Italy are Rome and Naples. At the Italian capitol and in its neighborhood we may study the volcanic Campagna with its beds of tuff (105) and its crater lakes (405. See Sir A. Geikie, The Roman Campagna, Landscape in History and other Essays, Macmillan, 1905, pp. 308-352; also Deecke, Sammlung Geologische Führer, Vol. 8, Campagna, 1901). From Rome it is an easy journey to the cataract of Tivoli with its deposits of travertine (184). In the opposite direction from Rome across the Campagna rise the Alban Hills, ruins of a composite cone with several crater lakes on the sites of former vents. On the summit of the encircling crater rim, like the Monte Somma of the Vesuvian Mountain now a crescent only, is located the chief Italian station for earthquake study.

From Naples we may reach in short excursions and study with some care still active volcanic mountains. To the east is Mount Vesuvius (94, 97, 122, 124, 127-137), which was in grand eruption in April, 1906. Westward from Naples are the Campi Phlegraeii, or burning fields, with many craters. Of these Astroni offers a fine example of a large-cratered cinder cone (105). In the same vicinity are Monte Nuovo (96) and the Solfatara (97), the latter a type of volcano which no longer erupts lava, but in its place emits carbon dioxide and other gaseous emanations (Grotto del Cane). The starting point for excursions in the Phlegræan fields is Pozzuoli with its Temple of Jupiter Serapis (254-255), reached from Naples by an electric line which pierces the wall of an immense crater (Posilippo) composed of fine yellow volcanic ash known as Pozzuolan.

From Naples steamers make short excursions to Sorrento with its deep ash deposits, and to Capri with its blue grotto (257-258). Herculaneum (139) and Pompeii (122), buried during the eruption of 79 A.D., are on the line of the Circum-Vesuvian Railway.

Steamships to New York from Naples call at Gibraltar, the land-tied island _par excellence_ (241). Most steamships of the southern route pass through or near the volcanic islands of the Azores, and certain boats touch at Algiers, from which a line of railway gives access to Biskra on the borders of the Desert of Sahara.

Throughout these pilgrimages the traveler should be on the alert to note not only the agent responsible for the features which come under his observation, but, especially where this is the common sculpturing agent of running water, he should not fail to notice the stage of the erosion cycle which is represented (Chapter XIII).

INDEX

Abrasion, beneath glaciers, 275.

Abyssinia, fissure eruptions in, 101.

Accordance, of tributary valleys, 162.

Adiabatic refrigeration, in relation to glaciers, 262.

Adolescence, in cycle of erosion, 169.

Advancing hemicycle of glaciation, 263-266.

Advective zone, of atmosphere, 270.

Aftershocks, of earthquakes, 83.

Agassiz, glacial lake, 325-328.

Agassiz, Louis, cited, 339, 400.

Age, of strata, 38, 52.

Aggradation, 162.

Aktian deposits, 36.

Alaskan coast, map of, 79.

Albs, 376.

Alden, W. C., cited, 316, 318, 319.

Algæ, growth of, in hot springs, 194.

“Alkali” in deserts, 201.

Alluvial bench, 214.

Alluvial cone, 213.

Alluvial-dam lakes, 423.

Alluvial fan, 213.

Alpine glaciers, 383, 386.

Alterations of minerals, 27.

Altitude, of different parts of lithosphere, 18.

American Falls, future extinction of, 357.

Amphiboles, 459.

Amphitheaters, formed on drift sites, 369.

Amundsen, R., cited, 23.

Analysis, of folds, 54.

Anderson, Tempest, cited, 146, 147.

Andersson, J. G., cited, 157, 295.

Andesite, 463.

Angular unconformity, 53.

Antarctica, 154, 281.

Antarctic protuberance, 17.

Antarctic shelf ice, 289, 290.

Anticlinal folds, 42.

Anticlines, 42; tension in, 45.

Anticyclone, glacial, 284.

Ants, factor in rock decomposition, 156.

Apron, alluvial, 213.

Aprons, outwash, 280, 281.

Arbenz, P., cited, 195.

Arches, of folded strata, 42; sea, 233, 234.

Architecture, of fractured earth superstructure, 55.

Arctic depression, 17.

Areal geological map, 62.

Arêtes, 373.

Arldt, Theodore, cited, 11, 19, 438.

Arnold, Ralph, cited, 157.

Arrangement of oceans and continents, 10.

Artesian wells, 190, 191, 196.

Ash, volcanic, 122.

Askja, eruption of, in 1875, 101.

Assmann, R., cited, 294.

Astronomical _vs._ geodetic observations, 12.

Atlantis, North, 16.

Atmosphere, compressibility of, 8.

Attack, of the weather, 149.

Atwood, W. W., cited, 7, 160, 298, 300, 313, 372.

Axial plane, of folds, 42.

Axis, of folds, 42.

Azurite, 453.

Bacteria, part taken in weathering, 156.

“Bad Lands”, control of relief in, 223, 224.

“Bad Land” topography, 214.

_Bajir_, 216.

Balance, between degradation and aggradation, 161.

Bandai-san, dissection of, 141.

Barchans, 211.

Barrancoes, 139.

Barrell, J., cited, 221, 447.

Barrier beaches, 240; sections of, 242; uplifted, 249, 250.

Barrier lakes, 420.

Barriers, 240; mountain, in relation to glaciers, 262.

Bars, 240.

Basal conglomerate, 37, 53.

Basalt, 463; faulted blocks of, 58; of Hawaii, 105.

Base level, 159.

Basin-range lakes, 402, 403.

Basin Range structure, 440.

Basins, flat bottomed, separating dunes, 216; of exudation, 272; of sedimentation, earlier, 38.

Bastin, E. S., cited, 210.

Batholites, 143.

“Bath tubs”, 395.

Beach pebbles, 239.

Beach sand, 206, 238.

Beaches, remaining from ice-dam lakes, 410; shingle, 239; storm, 240; uplifted, “feathering out” of, 344.

Bedded structure of rocks, 31.

Beede, J. W., cited, 195.

“Bee-hive” mountains, 380, 381.

_Belgica_ expedition, 289.

Belt of sea which divides land masses, 11.

Berghaus, H., cited, 424.

Bergschrund, 370.

Berson, A., cited, 294.

Berthaut, General, cited, 7.

“Bird-foot” delta, 167.

“Biscuit cutting” effect of glacial sculpture, 372.

Blackwelder, E., cited, 318.

Block mountains, 446.

Blocks, orographic, 58.

_Bocchi_, 125.

Bog, floating, 429.

Bogs, of peat, 429, 430.

Bonney, T. G., cited, 146.

Borax deposits, in deserts, 201.

Border drainage, about glaciers, 316, 320, 321.

Border lakes, 399, 414.

Bosses, 143.

“Bottoms”, from entrenched meanders, 173.

“Bowlder clay”, 310.

“Bowlder pavement”, 237.

Bowlders, faceted, 310; glacial, 298; “soled”, 276, 310; thrown up during earthquakes, 69.

Bowlder trains, 306.

Bowman, Isaiah, cited, 179.

Box cañons, 214.

Braided streams, 280.

Branner, J. C., cited, 6, 91.

“Bread-crust” lava projectiles, 119.

Breakers, 232.

Breccia, fault, 60.

Bridges, nature of damage to, during earthquakes, 75, 76.

Brigham, A. P., cited, 424.

Brögger, W. C., cited, 66.

Bruce, W. S., cited, 290, 382, 399, 414.

Bryant, H. G., cited, 289.

Buckley, E. R., cited, 433, 434.

Built terraces, 235.

Bunsen, cited, 192.

Burns, G. P., cited, 434.

Burton, W. K., cited, 92.

Buttes, 216.

Bysmalite, 442, 447.

Calcareous ooze, 36.

Calcareous sinter, 184.

Calcareous tufa, 464.

Calcite, 455.

Caldera, 405, of composite volcanic cones, 126.

Camiguin volcano, birth of, 96, 97.

Campbell, M. R., cited, 178.

Cañons, 160; box, 214.

Capri, blue grotto of, 257, 258.

Capture, river, 175, 176, 179.

Carbonization, 151.

Cascade Mountains, fissure eruptions of, 102.

Cascade stairway, 376.

Caspian Depression, 14.

Cauliflower cloud, 130.

Caverns, galleries directed by joints, 182; of limestone, 182, 195; refuge of predatory animals, 185.

Caves, sea, 234.

Cellular structure, of lava domes, 112.

Centers of dispersion, of North American Pleistocene glaciers, 298.

Centrosphere, 8.

Cerussite, 455.

Chaix, A., cited, 195.

Chaix, E., cited, 195.

Chalcopyrite, 453.

Challenger expedition, 38, 96, 97, 293.

Chamberlin, T. C., cited, 29, 156, 191, 196, 205, 221, 222, 293, 295, 318, 319, 337, 339.

Character profiles, coast, due to uplift or depression, 259; composite, 229; directly due to volcanic agencies, 145, 146; from stream erosion in humid climates, 177; of arid lands, 220; of shore features, 243; referable to continental glaciers, 318; referable to mountain glaciers, 379.

“Checkerboard topography”, 226.

Chemical sediments, 34.

Chicago outlet, 331.

Chimneys, in “driftless area”, 300.

Chimneys, shore feature, 234.

China, loess of, 207.

Chlorite, 458.

Chlorite schist, 465.

Cicatrice, from dissection of volcanoes, 142.

Cinder cones, 105; corrugations upon, 138; diameter of crater in relation to violence of explosions, 123; grander eruptions of, 117; profiles of, 123; secondary, 111.

Cinder eruptions, artificially simulated, 122.

Cirques, 371; life history of, 371; subordinate, 371.

Cities, destruction of, by drifting sand, 218.

Clastic rocks, 30.

Clay slate, 466.

Cleavage, mineral, 27, 450; rock, 44.

Clefts, volcanic, in Iceland, 99.

Cliffs, notched, 233.

Climatic conditions, in relation to mountain sculpture, 443.

Clinometer, 48.

Cloudbursts, in deserts, 201, 212.

Cloud zones, 268, 269, 294.

Coals, 466.

Coast, Dalmatian, grottoes of, 258.

Coast, elevation of, during earthquakes, 80; submergences of, during earthquakes, 80.

Coastal plains, 246; belted, 247.

Coast lines, even, 246; indicative of uplift or submergence, 245, 246; ragged, 246.

Coast records, 245.

Coasts, Atlantic and Pacific contrasted, 438; embayed, 251.

Coast terraces, 80, 250, 241; uplift, effect of, on sediments, 38.

Coats Land, shelf ice of, 290.

Cobalt, in meteorites, 23.

Cobb, Collier, cited, 179.

Coigns, of earth’s tetrahedral figure, 15.

Coleman, A. P., cited, 318.

Colk lakes, 408, 409.

Colks, scape, 277.

Collet, L. W., cited, 39.

Colorado desert, 74.

Color, of minerals, 450.

Cols, 374; origin of in cirque intersection, 372.

Comb ridges, 373.

Compass, geologist’s, 47, 48.

Competent layer, 42; in relation to lava reservoirs, 144.

Composite cones, _caldera_ of, 126, 127.

Composite groups of joints, 57.

Composite volcanic cones, 105.

Composition of earth, 29.

Composition of the earth’s core, 21.

Compression of a district during earthquakes, 76.

Cones, alluvial, 213; cinder, 105; composite volcanic, 105.

Conformable series, 51.

Conglomerate, 34, 463; basal, 37, 53.

Constructional topography, 309.

Construction of buildings, in earthquake regions, 89-91.

Continental glacier, behind rampart, 281; in Victoria Land, 280-285; of Antarctica, literature of, 295; of Greenland, 271; of Greenland, melting on margin of, 278; of Greenland, literature, 295.

Continental glaciers, contrasted with mountain glaciers, 266-268; defined, 266-267; of “ice age”, 297; of ice age, cross section of, 302; nourishment of, 283, 286, 295; profiles of, 267.

Continental platform, 19.

Continental shelves, 18, 19; origin, 232.

Continents, arrangement of, 10; development of, 14; increase in area of, through wave action, 241; past history of, 14.

Contortions of the strata, 40.

Contours, of topographic maps, 62.

Contraction of earth’s surface, during earthquakes, 74.

Contrary movements upon coasts, 254, 257.

Convective zone, of atmosphere, 270.

Conway, W. M., cited, 294.

Copernicus, cited, 10.

Copper glance, 455.

Coquina, 35.

Cornish, Vaughan, cited, 211, 222, 244.

Corrasion, 162.

Corrosion, of rocks, 156.

Coulée lakes, 406.

Coves, 233, 234.

Cracks, earthquake, 74.

Crater, evolution of form of, 128.

Crater lakes, 405, 406.

Craterlets, 84; sections of, 85.

Craters, mechanics of explosions in, 115.

Crater, volcanic, 95.

Credner, G. R., cited, 179.

Crescentic levee lakes, 416, 417.

Crestline, of an anticline, 42.

Crevasse, marginal, on mountain glaciers, 370.

Crevasses, in connection with river cut-offs, 164; on glaciers, 391.

Cross, Whitman, cited, 216, 441, 447.

Cross-bedded structure, 37.

“Crystal cellars”, 27.

Crystal form, of minerals, 449.

Crystals, behavior under special treatment, 24, 25; essential nature of, 23; forms of, 454, 457; individuality of, 24; mutilated, later growth of, 26; symmetry of form of, 23.

Crustal shortening, 42.

Cuestas, 246, 247; south of Lake Ontario, 361, 362.

Cut and built terrace, on steep shore of loose materials, 237.

Cut-offs, of meanders, 164.

Cut rock terraces, 235.

Cuvier, cited, 199.

Cvijić, J., cited, 195.

Cycle of glaciation, 263, 294.

Cycles, of glaciation, Pleistocene, 297; of stream meanders, 163.

Dana, J. D., cited, 6, 104, 106, 109, 111, 146, 147.

Dana, E. S., cited, 29.

Daly, R. A., cited, 447.

Dante, cited, 9.

Darton, N. H., cited, 179.

Darwin, Charles, cited, 199, 322, 323, 339.

Daubrée, A., cited, 54.

David, T. W. E., cited, 23.

Davis, C. A., cited, 434.

Davis, W. M., cited, 7, 178, 179, 221, 247, 276, 317-319, 378, 382.

Deceptive unconformity, 53.

Decomposition, 149, 156; mechanical results of, 150.

Débris cones, 395.

Deep sea deposits, 36, 38.

Deflation, 204.

Deforestation, in relation to agriculture, 156; of Karst region, 188; relation to erosion, 157.

Degeneration, 149.

De Geer, G., cited, 351, 366, 410.

Degradation, 161, 162.

Dekkan, fissure eruptions of, 101.

Delebecque, A., cited, 424.

De Lorenzo, cited, 125, 132.

Delta, “Bird-foot”, 167; bottom-set beds, 167; dry, 213; of Mississippi River, rate of growth of, 168.

Delta deposits, manner of growth of, 167.

Delta lakes, 419, 420.

Delta region, of a river, 35.

Deltas, abnormal, below outlets of lakes, 431; in relation to agriculture, 166; in relation to population, 166; lake, 428; of rivers, 165, 166, 179; sections of, 168.

Dendritic glaciers, 383, 385, 386.

Deniston, cited, 121.

Deposition, in zones about desert, 216, 217.

Deposits, aktian, 36; chemical, 34; continental, 37; deep sea, 36, 38; delta, manner of growth of, 167; fluviatile, 35; fluvio-glacial, 31, 310; in valley vacated by glacier, 398; glacial, 31; lacustrine, 35, 217; littoral, 36; marine, 35; mechanical, 34; organic, 34; salt, 217; shoal water, 26; sinter, 184; terrigenous, 36.

Derangement of water flow, during earthquakes, 83, 84.

Derwies, V. de, cited, 447.

Descent of ground water, 180.

Desert, due to deforestation, 156; erosion in, 214, 222; law of, 197.

Desert lakes, 423.

Desert landscapes, features in, 209.

Desert rains, 212.

Desert rocks, red color of, 222.

Desert varnish, 201, 222.

Deserts, former shore lines in, 198; self-registering gauge of past climates, 198.

Destructional topography, 309.

Detection of plunging folds, 49, 50.

Detonations, during Vulcanian eruptions, 131.

Device, to simulate building of cinder cones, 122.

Diabase, 462.

Diagram, to illustrate formation of lava reservoirs, 143.

Diagrams for comparison of fold types, 42; to show the effect of spheroidal weathering, 150.

Diamonds, in the drift, 307.

Diffission, 204.

Dikes, hollow, 140; in China, 167; in Holland, 166; from volcanic dissection, 140.

Diller, J. S., cited, 39, 425.

“Diluvium”, 305.

Dimples, on margin of continental glaciers, 272.

Dip, 46.

Dirt cones, 396.

Disintegration, 156; of rocks in deserts, 202; through root expansion, 154; through tree growth, 154, 155.

Dislocations, marginal, about deserts, 212.

Dispersion of the drift, 304-309, 319.

Displacement, total, on faults, 59.

Dissection of volcanoes, 139.

Distributaries, on alluvial fans, 213, 220.

Divides, 170; migration of, 175.

Dolines, of Karst region, 187, 422.

Dolomite, 465.

Dolomites, 203, 228, 445.

Domed mountains of uplift, 441.

Dome structure, of granite masses, 152, 157.

Domes, lava, 105.

Dovetailing, of sea and land, 11, 17.

Drainage, changes of, due to glaciation, 336-338; haphazard, of glaciated area, 301; interference of glaciers with, 320; of glaciers, 397; reversals of, due to glaciation, 337, 338; trellis, 175.

Drainage lines, control of, by fractures, 224.

Drainage networks, controlled by fractures, 225, 226; repeating pattern in, 225.

Drake, Sir Francis, circumnavigation of the globe, 10.

_Dreikanten_, 205.

Driblet cones, 104, 125; of Kilauea, 107.

“Drift”, 305.

Drift, assorted, 309; dispersion of, 304-309; englacial, 277, 278; unassorted, 309.

“Driftless area”, 300, 313, 318.

Driftless area, map of, 298.

Drift sites, 368, 369.

Drowned rivers, 251.

Drumlins, 311, 316, 317, 399.

Dry deltas, 213.

Drygalski, E. von, cited, 273, 279, 295, 296.

Dry weathering, in deserts, 201.

Dune, war with oasis, 216.

Dune lakes, 421.

Dunes, 222; forms of, 210, 211; in relation to obstructions, 209, 210; stopped by vegetation, 211; wandering, 209, 211.

Dust, carried out of desert, 206, 222; volcanic, 122.

Dust wells, 395.

Dutton, C. E., cited, 85, 92, 178, 200, 222, 447.

Earlier figures of the earth, 14.

Earth, a magnet, 23; composition of, 20; oblateness of, 10; rigidity of, 20, 21, 29; scale of its elevations, 10, 11; theories of origin of, 20, 29; surface shell, chemical constitution of, 23; surface shell, response to load, 340.

Earth features, shaped by running water, 169.

Earth figure, evolution of ideas concerning, 9.

Earthquake cracks, 74.

Earthquake fountains, 190.

Earthquake lakes, 404.

Earthquake, of Alaska, 1899, 72, 77, 79, 80, 81; of Assam, 1897, 72, 77; of California, 1906, 70, 72, 73, 74, 90, 91; of Casamicciola, 1883, 87; of Costa Rica, 1910, 68; of India, 1819, 84; of Jamaica, 1692, 80; of Jamaica, 1907, 80; of Japan, 1891, 72, 75; of lower Mississippi Valley, 1811, 83; of Messina, 1908, 68; of Owens Valley, California, 1872, 73, 77, 78, 79; of Servia, 1904, 84; of South Carolina, 1886, 85.

Earthquake shocks, heavy over loose foundations, 88.

Earthquakes, aftershocks of, 83; associated with growing mountains, 86; changes in earth’s surface during, 71; connected with lines of fracture, 86; descriptive reports upon, 92; due to adjustments between blocks of shell, 78, 79; faults and fissures, 71; focused at fault intersections, 87; fountains during, 83, 86; localized at corners of earth blocks, 87; manifestations of changes in level, 68; nature of shocks, 67; of Ischia, localization of, 87; shown by coast terraces, 250; special lines of heavy shock, 86; in unstable areas of earth’s crust, 86; wave motions of, 68; zones in distribution of, 86.

Earth relief, repeating patterns in, 223.

Eckert, cited, 188.

Effect of contraction upon a spherical body, 13.

Egg-spinning demonstration of earth rigidity, 20.

“Elevation-crater” theory of volcanoes, 95, 139.

Embankments, shore, 240.

Embayed coasts, 251.

Emerson, B. K., cited, 19.

End moraines, 394.

Engell, M. C., cited, 296.

Englacial débris, 393.

Englacial drift, 277, 278.

_Entonnoirs_, 182.

Entrenchment of meanders, 172, 173, 179.

Eolian sand, 206.

Eolian sediments, 30.

Erosional unconformity, 53.

Erosion cycle, 159.

Erosion, effect of, in adding curves to landscape, 65; glacial, in contrast with normal weathering, 377; in desert, 214; shadow, 206; stream, as modified by resistant rocks, 174.

“Erratic blocks”, 304.

Eruptions, Strombolian, 117; Vulcanian, 117, 125.

Escarpments, from faults, 59.

Eskers, 311, 315, 316, 363.

Estes, L. A., cited, 93.

Estuaries, 251.

Etna, eruption of 1669, 122.

Evolution, doctrine of, in connection with fossils, 38.

Evolution of ideas concerning the earth’s figure, 9.

Exfoliation, 151, 203.

Expanded foot glaciers, 383, 385.

Experiment, to illustrate relation of earthquake shocks to foundations, 88.

Experiments, on fracture and flow, 40, 41; for demonstration of earthquakes, 81, 82.

Exposures, rock, 46.

Extrusive rocks, 463.

Fairbanks, H. W., cited, 155, 170, 174, 201, 205, 214, 224, 248, 249, 250, 260, 302, 375, 406, 413, 429.

Fairchild, H. L., cited, 339.

Falls, “Bridal veil”, 378.

Falls, ribbon, 378.

Fan, alluvial, 213.

Farrington, O. C., cited, 29.

Fault, drag upon, 60.

Fault breccia, 60.

Fault topography, 65.

Faults, 58, 440; during earthquakes, 71; earthquake, change in throw upon, 76, 77, 78; earthquake, disappear in loose materials, 73; earthquake, of small displacements, 74; earthquake, plan of, 76, 78; illusory nature of, 59; methods of detecting, 59; post-glacial, 74; relation of escarpments to, 60; shown by changes in strike and dip, 61; shown by offsets, 61.

Feldspars, 456.

Fenneman, N. M., cited, 424, 425.

Festoons of mountain arcs, 435, 436.

Field ice, 286.

Field map, geological, 62, 63.

Figure of the earth, the, 8.

Figures, earlier, of the earth, 14; earth, evolution of, 15.

Figure toward which the earth is tending, 12.

“Fire girdle” of the Pacific, 98.

Firn, 369.

Fissure eruptions, of volcanoes, 101.

Fissures, during earthquakes, 71; earthquake, 74; in connection with volcanoes, 99-101.

Fissure springs, 61, 190, 195.

Fjords, 290, 340.

“Float copper”, 305.

Flooded portions of continents, 18.

Flood plain, 178; manner of grading of, 162.

Floors of hydrosphere and atmosphere, 18.

Flow, experiments on, 41; zone of, 40.

Flow texture, of extrusive rocks, 33.

Fluviatile deposits, 35.

Fluvio-glacial deposits, 31.

Fluxion texture, of extrusive rocks, 33.

Folds, analysis of, 54; comparison of shapes of, 44; mutilated, restoration of, 45; pitching, 43; secondary, 44; shapes of, 43.

Fold topography, 65.

Forbes, J. D., cited, 294.

Fore-set beds, 167.

Forest, destruction of, in relation to agriculture, 156.

Formation of lava reservoirs, 143.

Formations, measurement of thickness of, 48, 49.

Fort Snelling, on Warren River, 327, 331.

Fosses, glacial, 281, 314; in connection with peat bogs, 430.

Fracture control, of drainage lines, 224.

Fracture, experiments on, 41; of minerals, 450; zone of, 40, 46.

Fractures, in rocks, shown by rectilinear lines on map, 65; system of, 55.

Free, E. E., cited, 222.

Free waves, 232.

Fretted upland, 372, 373.

Frost, prying work of, 152.

Frost action, 223.

Frost snow, 285.

Fuller, M. L., cited, 157, 195.

Fumeroles, 97.

Gabbro, 462.

Gabled façade, in desert landscapes, 221, 443.

Galenite, 453.

Gannett, Henry, cited, 178, 386.

Gaps, water, 176; wind, 176.

Garnet, 459.

Gautier, E. F., cited, 221.

Geikie, A., cited, 6, 7, 148, 178, 244, 318.

Geikie, James, cited, 6, 318.

Geoid, departure from spherical surface of, 10.

Geological map, 46, 54; areal, 62, 63; base of, 61; field, 62, 63.

Geological section, 46, 47.

Geology, defined, 1.

Geyserite, 194.

Geysers, 191-194; effect of plugging with sod, 193; in relation to drainage lines, 191; soaping of, 194.

_Geysir_, 192.

Gilbert, G. K., cited, 93, 148, 157, 178, 179, 198, 221, 224, 240, 244, 294, 344, 345, 347, 350, 355, 356, 357, 358, 359, 362, 366, 370, 381, 434, 446, 447.

_Gjás_, volcano fissures in Iceland, 99.

Glacial anticyclone, 284.

Glacial deposits, 30, 31.

Glacial fringe, of Grant Land, 285.

Glacial Lake Agassiz, 325-328, 339.

Glacial lakes, at close of ice age, 320; of St. Lawrence Valley, 329.

Glaciated regions, aspects of, 302; characteristics of, 301; contrasted with nonglaciated, 299, 309.

Glaciation, conditions essential to, 261; cycle of, 263; Permo-Carboniferous, 298.

Glaciations, following changes in earth’s figure, 15; previous to “ice age”, literature of, 318.

Glacier broom, over continental ice, 285.

Glacier cornices, 397.

Glacier deposits, upon its bed, 390.

Glacier drainage, 397.

Glacier flow, 390, 400; data from accidents to Alpinists, 392.

Glacier gravings, 301, 319; multiple records, 304.

Glacier lobe lakes, 411.

Glacier milk, 398.

Glacier mills, 278.

Glacier pavement, 276.

Glaciers, birth of, 369; crevasses on, 391; dendritic, 383, 385, 386; grinding tools of, 276; horseshoe, 383, 386, 387; inherited basin, 387-389; initiation of, 262; in relation to wind direction, 262; main types of, 266; mountain, cross sections of, 394; mountain, expanded-foot type, 264; mountain, land sculpture by, 367; mountain, successive stages, 383; nivation, 387; nourishment of, 268-270; piedmont, 383, 384; radiating, 383, 386; sensitiveness to temperature changes, 263; séracs, 391; surface features of, 390; tide water, 290, 386.

Glacier stars, 395.

Glacier tables, 395.

Glacier types, successive, during waning glaciation, 383.

Glacier wells, 278.

Glassy texture, of extrusive rocks, 32.

Glen Roy, 322, 339.

Glint, 409.

Glint lakes, 408, 409.

Gneiss, 465.

Gneiss banding, 31.

Goethe, cited on volcano structure, 139.

Gold, E., cited, 294.

Goldthwait, J. W., cited, 259, 320, 341, 345, 351.

Gondwana Land, 16.

Gorges, through rock bars, 378.

Grabau, A. W., cited, 361, 366.

Grading of flood plain, 162.

Grand Cañon of the Colorado, 146, 169, 174, 215, 443.

Grand River outlet, 333.

Granite, 462; dome structure in, 152, 157.

Granite domes, 221.

Granitic texture, of igneous rocks, 33.

_Grats_, 373.

Gravel, kame, 310.

“Gravel piedmont”, 214.

Great Basin, 190, 198, 439.

Great Lakes, probable future of, 347, 348; submergence of certain shores of, 349, 350.

Great Ross Barrier, 282.

Great Salt Lake, 199; fluctuations of level of, 198.

Green, W. Lowthian, cited, 19.

Gregory, J. W., cited, 11, 19, 439, 446.

Grooved upland, 372, 373.

Gross, H., cited, 294.

Grossman, cited, 268.

Grottoes, sea, colors of, 258.

Ground water, 180; descent of, in relation to joints, 181.

Ground water lakes, 424.

Grund, A., cited, 195.

Gullies, early stages of, 160.

Gulliver, F. P., cited, 244, 319.

Gullying process, started by deforestation, 156.

Gypsum, 455.

Hade, on faults, 59.

Hague, Arnold, cited, 196.

Halemaumau, Kilauea, 107, 108.

Hamilton, Sir William, cited, 128.

Hanging valleys, 378.

Hardness, of minerals, 451.

Harwood, W. A., cited, 294.

Haug, E., cited, 7, 133, 211.

Haughton, Samuel, cited, 56.

Hawaii, lava domes of, 105; lava surfaces of, 113; map of, 106; section through, 106.

Hayes, C. W., cited, 156.

Headlands, notched, 341.

Heave, of faults, 59.

Hebrews, conception of the universe, 9.

Hedin, Sven, cited, 221.

Heilprin, A., cited, 148.

Heim, A., cited, 54.

Heligoland, 236.

Helland, A., cited, 99.

Hematite, 452.

Hemicycles, of glaciation, 263, 264.

Herculaneum, buried beneath mud flows, 139.

Hess, H., cited, 267, 272, 294, 393, 400.

High plains, 435; origin of, 219.

Hilgard, E., cited, 222.

Hinge lines, of uptilt, 344-347.

Hitchcock, C. H., cited, 106, 147, 434.

Hobson, B., cited, 120.

Hogarth, William, cited, 170.

Hogarthian line of beauty, in landscapes, 170-171.

“Hog backs”, 442.

Holmes, W. H., cited, 441.

Horns, 374.

Horseshoe glaciers, 383, 386, 387.

Hot springs, 191; colors in, due to algæ, 194.

Hovey, E. O., cited, 136, 137, 148.

Hovey, H. C., cited, 183, 195.

Howchin, W., cited, 298.

Howe, E., cited, 140.

Howell, cited, 325.

Hudson River, narrows of, 174.

Hudsonian channel, 252.

Hummocks, on pack ice, 286.

Humphrey, R. L., cited, 90, 93.

Humphreys, cited, 404.

Humus, in relation to weathering, 156.

Huntington, Ellsworth, cited, 216, 217, 221, 222.

Hus, H. T. A. de L., cited, 183.

Hydration, 151.

Hydrosphere, 8.

Hypothesis, the value of, 6; Laplacian, of the universe, 20.

Icebergs, 296; Antarctic, 292, 293; Antarctic, formation of, 292; blue, 292; manner of formation of, 291, 292; northern, 291.

Ice caps, profiles of, 267, 268; sculpture, 380.

Ice-dammed lakes, 321, 323, 410, 411; in St. Lawrence Valley, 339; of Scottish glens, 322.

Ice floes, 287.

Iceland, fissure eruptions of, 102.

Ice pyramids, 395.

Ice ramparts, 431-434; manner of formation of, 433.

Igneous rocks, 30; textures of, 32.

Imlay outlet, 332.

Inbreak, of lava surface, 107.

Incised topography, 301.

Inherited basin glacier, 387-389.

Interlobate moraines, 314.

Inter-pluvial periods, 198.

Intricate pattern of river etchings, 158.

Intrusive rocks, 32, 462.

Islands, land-tied, 241; steep rocky, due to submergence, 252.

Isobases, 347.

Isoclinal folds, 42.

Isothermal zone of atmosphere, 270.

Jagger, T. A., Jr., cited, 148.

Jamieson, T. F., cited, 221, 322, 339.

Jeannette exploring expedition, 287, 295.

Jensen, H. I., cited, 110, 113, 147.

Johnson, D. W., cited, 7, 148.

Johnson, W. D., cited, 77, 213, 219, 220, 222, 370, 381.

Johnston-Lavis, H. J., cited, 87, 131, 132, 134, 138, 147, 148.

Joint blocks, in Niagara limestone, 353.

Joint plane, seat of frost action, 370.

Joints, 56; effect on surface features, 57; closed during earthquakes, 76; composite nature of, 58; composite groups of, 57; disorderly, 57; displacements upon, 58; master, 56; space intervals of, 58; sets of, 55; system of, 55.

Joint series, combinations of, 56.

Joint systems, 66.

Jorullo, birth of, 96.

Judd, John W., cited, 116, 118, 139, 148.

Julien, A. A., 156.

Jura Mountains, 46.

Kame gravel, 310.

Kames, 311, 314.

Kammerbühl, 139.

_Karrenfelder_, 188.

Karst, characters of, 186-187; once forested, 188.

Karst conditions, 195.

Karst lakes, 422.

_Katavothren_, 188.

Katzer, F., cited, 195.

Kearney, Th. H., cited, 222.

Kelvin, Lord, cited, 20, 29.

“Kettle moraines”, 311-314.

“Kettles” on moraines, 312.

Kikuchi, Y., cited, 148.

Kilauea, 101, 106; draining of lava in crater of, 108; eruption of 1840, 109, 111, 112; lava movements in, 106, 107; moving platform in crater, 107; range in height of lava in, 107.

King, F. H., cited, 157, 195.

Knebel, W. von, cited, 185, 195, 258, 260.

“Knob and basin” topography, 314.

Knott, C. G., cited, 92.

Kopisch, August, cited, 258.

Kotô, B., cited, 92.

Krakatoa, dissected by eruption, 142.

Krakatoa, eruption of 1883, 141, 142.

_Kuppen_, 105.

Kurische Nehrung, wandering dunes of, 210.

Laboratory apparatus, for simulation of cinder eruptions, 122.

Laboratory models, for study of geological maps, 63.

Laccolites, 143, 441, 442, 447.

Lacroix, A., cited, 148.

Lacustrine deposits, 35.

Lake Agassiz, glacial, 325-328.

Lake Algonquin, 334, 342.

Lake Arkona, 332, 333.

Lake basins, study of, 401.

Lake Bonneville, 199.

Lake Chicago, 330, 332, 333.

Lake Eulalie, draining of, during earthquake, 83.

Lake Iroquois, 334, 335.

Lake Maumee, 330, 331, 332, 345.

Lake Ojibway, glacial, 338.

Lake stages, in St. Lawrence Valley, 336.

Lake Warren, 333, 334.

Lake Whittlesey, 332, 333.

Lakes, alluvial dam, 423; as regulators of air temperature, 431; as regulators of river flow, 431; as settling basins, 426-428; barrier, 420; basin range, 402, 403; become extinct through wave action, 428; border, 399, 414; classification of, 424; colk, 408, 409; continental glaciation, 424; coulée, 406; crater, 405, 406; crescentic, 329, 330; crescentic levee, 416, 417; currents in, 431; delta, 419, 420; desert, 424; drained by cutting down of outlet, 428; dune, 421; drained during earthquakes, explanation of, 83; earthquake, 404; ephemeral existence of, 426; extinction by peat growth, 429-430; extinction of, in desert regions, 430; fresh water, 401; glacier lobe, 411; glint, 408, 409; ground water, 424; ice dam, 410, 411; intramorainal, about continental glaciers, 279, 280; karst, 422; landslide, 414; morainal, 315, 406, 407; mountain glaciation, 424; newland, 401, 402; ox-bow, 165, 415; pit, 315, 407, 408; playa, 422; raft, 417, 418; rift-valley, 403, 404; river, 424; rock basin, 376, 377, 400, 412; rock basin about continental glaciers, 279; rôle of, in economy of nature, 430; saline, 401; salines, 423; saucer, 415, 416; seasonal, 189, 422; side delta, 326, 327, 418, 419; sink, 421; strand, 424; tectonic, 424; valley moraine, 400, 413; volcanic, 424; “wall”, 432.

Laki, eruption in 1783, 99.

Laminated structure, of rocks, 31.

Lamplugh, G. W., cited, 225.

Land, growth of, from volcanic outflow, 113, 114; sliced during earthquake, 80; uptilt of, at close of ice age, 340.

Land areas, concentration of, in northern hemisphere, 11.

Land sculpture, by mountain glaciers, 367; in relation to climatic conditions, 443; referable to ice caps, 380.

Land shields, 15.

Landslide lakes, 414.

Land-tied islands, 241.

Lane, A. C., cited, 148.

Lankester, E. Ray, cited, 260.

La Noe, G. de, cited, 7.

_Lapilli_, 119, 122.

Laplacian hypothesis of the universe, 20.

Lateral moraines, 393.

Lateral movements, deep seated, during earthquakes, 81.

Lava, 32; block, 113; composition and properties of, 103; discharging from tunnel, 111; fluidity of basic, 103; movements, in caldron of Kilauea, 107; probable origin from shale, 144; ropy, 113; viscosity of siliceous, 103.

Lava domes, probable structure of walls of, 112; slopes of, 103, 104, 105.

Lava projectiles, pear-shaped type, 121.

Lava reservoirs, formation of, 143.

Lava streams, appearance of, 133, 134.

Lava surface, 113, 124.

Law of the desert, 197.

Lawson, A. C., cited, 92, 260, 351.

Leads, in pack ice, 286.

Le Conte, Joseph, cited, 6.

Leffingwell crater, California, 104.

Levees, 166.

Leverett, Frank, cited, 6, 104, 166, 312, 318, 321, 330, 332, 333, 334, 337, 339, 344, 345.

Lewiston escarpment, at Niagara, shaping of, 360-362.

Libbey, W., cited, 274.

Life histories, of rivers, 158.

Light figure, from surface of crystal, 25.

Lightning, in connection with volcanic eruptions, 130.

Limbs of faults, 59; of folds, 43.

Limestone, 464; origin of, 36; sinks, 182.

Limestone, caverns of, 182.

Limonite, 452.

Linck, G., cited, 122.

Lindenkohl, A., cited, 260.

Lineaments, 87, 226, 227.

Line of beauty, Hogarthian, in landscapes, 170, 171.

_Lithodomus_, borings of, in records of oscillation, 254.

Lithosphere, a complex of interlocking crystals, 25; and its envelopes, 8.

Littoral deposits, 36.

Loess, 35, 207; erosion of, 208.

Loessmännchen, 208.

Lubbock, Sir John, cited, 7.

Luray caverns, Virginia, 186.

Luster, of minerals, 450.

Lyell, Sir Charles, cited, 7, 96, 146, 199, 259, 260, 304.

_Maare_, 405.

McGee, W. J., cited, 157, 259.

Mackinac Island, records of uplift of, 341-344.

Madison, Wisconsin, 233, 237, 241, 317, 434.

Magellan, circumnavigation of globe, 9.

Magma, defined, 30.

Magnetism, of minerals, 451.

Magnetite, 452.

Malachite, 453.

_Mamelons_, 105.

Mammoth Cave, 182, 183.

Mantle, rock, 155.

Map, contour, nature of, 467; of Armorican mountains, 438; of barrier beaches, 242-243; of bowlder train from Iron Hill, 306; of cirques and niches, in Bighorn Mountains, 371; of coast lines, 246; geological, 54, 61; geological, method of preparing, 46, 63; of continental divide in Colorado, 377; of continental glacier in Victoria Land, 282; of Dalager’s nunataks, 277; of expanded foot glaciers, 264; of front of Green Bay lobe, 317; of glacial features, Southern Finland, 315; of glacial Lake Agassiz, 325, 326, 328; of glaciated area, Europe, 299; of glaciated area, North America, 298; of ice ramparts on Lake Mendota, 434; of inner Sandusky Bay, 350; of Kilauea and neighboring slopes, 109; of Lake Chicago and later Lake Maumee, 332; of Lake Maumee, 330; of Lakes Whittlesey and Saginaw, 333; of lava outflows on Vesuvius, 1906, 131; of lava streams on Mauna Loa, 126; of marginal moraines, 312; of mountain arcs of Eastern Asia, 438; of mountain arc of Sewestan, 436; of North Polar regions, 288; of part of “fire girdle” of the Pacific, 98; of Scottish glens, 322-324; of Volcano, 118; of volcano belts, 98; of Warren River, 326, 327; topographical, 61; topographical, preparation of, 467, 468; topographical, verification of, 469; to show dispersion of diamonds in Lake region, 308; to show dispersion of peculiar rocks, 305; to show distribution of existing glaciers, 263; to show formation of shore features, 238; to show glaciated areas of Pleistocene period, 297; to show reciprocal relation of land and sea, 11.

Marble, 466.

Margerie, Emm. de, cited, 7, 54.

Marginal moraines, 278-280, 311-314.

Marine clays, as marks of uplift, 253.

Marine deposits, 35.

Märjelen Lake, 329, 411.

Marks, of origin of rocks, 30; of uplift, on coasts, 245.

Marr, John E., cited, 7, 445.

Martel, E. A., cited, 181, 187, 195.

Martin, Lawrence, cited, 77, 92, 260, 280, 351.

Martonne, E. de, cited, 7, 195, 222, 382.

Massive structure, of rocks, 31.

Master joints, 56.

Matavanu, eruption in 1906, 110, 113, 147.

Mat of vegetation, shield to lithosphere, 155.

Matthes, F. E., cited, 7, 371, 381.

Maturity, of upland, 170.

Mauna Loa, 106; eruptions of, 109.

Meander scars, 165.

Meanders, entrenchment of, 172, 173, 179; stream, 163; stream, undermining by, 164.

Measurement of thickness, of formations, 48, 49.

Mechanical sediments, 34.

Medial moraines, 393; from nunataks, 274.

Mediterranean seas, 14.

Melting, selective, on glacier surface, 394.

Melville, G. W., cited, 289.

Mercalli, G., cited, 89, 117, 119, 147.

Merrill, George P., cited, 156.

Mesa, 215, 216; origin of, 112.

Metamorphic rocks, 30, 31, 465.

Meteorites, compared with earth, 22; composition of, 21, 23.

Mica, 458.

Mica schist, 465.

Michailovitch, J., cited, 84.

Microscopical petrography, 27.

Migration, of divides, 175.

Mill, H. R., cited, 424.

Mills, glacier, 398.

Milne, John, cited, 75, 92, 93.

Mineral fragments, possibility of growth of, 24.

Minerals, alterations of, 27, 28; common, properties of, 452-461; of economic importance, 452-456; important as rock makers, 456-461; properties of, 26, 27; quick determination of, 449.

Mississippi River, 167.

Mitchell, G. E., cited, 157.

Moats, about nunataks, 273, 274.

Models, laboratory, for study of geological maps, 63.

Mojsisovics von Mojsvár, E., cited, 228.

Mokuaweoweo, crater of, 106.

“Mole-hill” effect, after earthquakes, 73.

Molten rock, rise to earth’s surface, 94.

Monadnocks, 172.

Monte Nuovo, 96.

Monte Somma, _caldera_ of, 127.

Montessus de Ballore, de F., cited, 92, 93.

Monti Rossi, crystal rain from, 122; parasitic cones of, 125.

Mont Pelé, post-eruption stage of, 135-138; spine of, 136, 137, 138.

Moore, W. H., cited, 294.

Morainal lakes, 315, 406, 407.

Moraines, interlobate, 314; lateral, 393; marginal, 278-280; medial, 393; medial, from nunataks, 274; of mountain glaciers, 393, 394; recessional, 399; surface, 277; terminal, 311-314, 394; water-laid, 330.

Moreno, F. P., cited, 235.

Moseley, E. L., cited, 350, 351.

Moselle River, with entrenched meanders, 173.

Motive power, of rivers, 158.

Moulins, 398.

Mountain arcs, festoons of, 435, 436; theories of origin of, 436, 437.

Mountain glaciation lakes, 424.

Mountain glaciers, contrasted with continental glaciers, 266-268; defined, 266-268; dendritic, 383, 385, 386; expanded-foot type, 264; horseshoe, 383, 386, 387; land sculpture by, 367; marks of, 400; piedmont, 383, 384; profiles of, 267; radiating, 383, 386; studies of special districts, 294; summary of types of, 389.

Mountain ramparts, about continental glaciers, 271.

Mountains, battlement type, 228, 445; block type, 439; carved from plateaux, 442; of circumvallation, 442, 445; defined, 435; domed, of uplift, 441; erosional, 445; evidence for occupation by mountain glaciers, 400; genetical, 445; largely shaped by erosion, 435; of outflow and upheap, 440; origin and forms of, 435; truncated at coast lines, 438.

Mt. Etna, 125, 126.

Mt. Vesuvius, 94; appearance of, from Naples at night, 129; ash curtain, during eruption, 132; ash-fall over, 1906, 133; “cauliflower” cloud over, 133; changed appearance after eruption of 1906, 132; eruption of 79 A.D., 97; eruption of 1872, 124; eruption of 1906, 127-137; history of, 97; lavas of, 32.

Mud cones, 84; aligned upon a fissure, 84.

Mud-crack structure, 37.

Mud, flocculent calcareous, of Florida, 36.

Mud flows, which destroyed Herculaneum, 139.

Mud veneer, from eruption of Taal, 121.

Muir, John, cited, 7.

Munthe, H., cited, 313, 351, 410.

Murray, Sir John, cited, 39, 293.

“Mushroom rocks”, 205.

Nansen, F., cited, 17, 260, 271, 272, 287, 295.

Narrows, river, 174, 327.

Natural Bridge, near Lexington, Virginia, 184.

Natural bridges, 184.

Natural sand blast, 204.

Nature of materials in the lithosphere, 20.

Necks, volcanic, 140.

Nephelite, 459.

Neumayr, Melchior, cited, 7, 146, 195, 196, 222, 425.

Névé, 369.

Newborn glacier, 387.

Newland, 159, 247.

Newland lakes, 401, 402.

New Madrid earthquake, 83.

New River, of Cumberland plateau, 173.

Niagara Falls, 352-366; episodes in history of, 362-365; the clock of recent geological time, 364.

Niagara gorge, 352-366; drilling of, 353, 355; episodes in history of, in connection with glacial lakes, 364; plan and section of, 355; rate of recession of, 356.

Niches, 371; beneath snowdrift sites, 368, 369.

Nickel, in meteorites, 23.

_Nieves penitentes_, 397.

Nipissing Great Lakes, 335, 342.

Nipissing outlet, 335, 336.

Nippur, sand mounds over, 218.

Nivation, 368.

Nivation glacier, 387.

Noble, F. H., cited, 147.

Nordenskiöld, Otto, cited, 154, 157, 295.

North Atlantis, 16.

North Bay outlet, 335.

Northwest Highlands of Scotland, thrusts of, 45.

Norway, repeating patterns of, 229.

Notched cliffs, 233; elevated, 248.

Nourishment of continental glaciers, 295.

Nunataks, 272, 274, 277.

Nussbaum, F., cited, 161.

Oasis, 216.

Oblateness, of the earth, 10.

Observational geology _vs._ speculative philosophy, 5.

Obsidian, 463.

Obsidian Cliff, 33.

Ocean of Tethys, 16.

Oceanic platform, 19.

Oceans, arrangement of, 10.

Oldham, R. D., cited, 72, 76, 92.

Oldland, 159, 247.

Olivine, 461.

Omori, F., cited, 147.

Oölite, 464.

Oölitic limestone, 464.

Ooze, calcareous, 36; composition of, 39.

Optical mineralogy, 27.

Order of deposition, during marine transgression, 37.

Order of superposition, of strata, 52.

Organic sediments, 34.

_Orgeln_, 182.

Orleans, Duc d’, cited, 286.

Orographic blocks, 58.

Osar, 311, 315, 316.

Oscillations of movement, on coasts, 253.

Outcrop blocks, for study of maps, 63.

Outcroppings, 46.

Outlets, from continental glaciers, 271; of glacial lakes, 326, 327.

Outwash plains, 280, 281, 311, 313, 314, 399, 408.

Overthrust, 45.

Owens Valley, California, map of earthquake faults in, 78.

“Ox-bow”, of river, 165.

Ox-bow lakes, 165, 415.

Pack, drift of, 287; the, 286.

Pack ice, 286.

Pagination, of the earth record, 38.

_Pahoehoe_ type of lava surface, 113.

Pan form of deserts, 197.

Panum crater, _caldera_ of, 126.

“Parallel roads”, of Scottish glens, 322-325, 328, 339.

Partially dissected upland, 160.

Passarge, S., cited, 221, 222.

“Paternoster lakes”, 376.

Pattern, of river etchings, 158.

Patterns, repeating, 223.

Pavement, bowlder, 237; glacier, 276; tessellated from soil flow, 154.

Pavlow, A. P., cited, 108.

Peale, A. C., cited, 195, 196.

Peary, R. E., cited, 17, 283, 289, 295, 296.

Peat, 465; formation of, 429, 430.

Peat bogs, 429.

“Pelé’s Hair”, 107.

Pelé, spine of, 148.

Penck, A., cited, 294, 399, 414.

Peneplain, 171, 179.

“Penitents”, 397.

“Perched bowlders”, 306.

Peridotite, 462.

Periods, interpluvial, 198; pluvial, 198.

Peripheral granulation, 31.

Perret, F. A., cited, 148.

Philippi, E., cited, 295.

Phillips, John, cited, 56.

Physiographic models, preparation, of, 470.

Piedmont glaciers, 383, 384.

_Pino_, 119, 130.

Pipes, volcanic, 140.

Piracy, river, 175, 176.

Pirsson, L. V., cited, 39, 447.

Pitch, 43.

Pitching folds, 43.

Pit lakes, 315, 407, 408.

Pitted plains, 314, 407, 408.

Pittier, H., cited, 405.

Plains, flood, 178; coastal, 246; outwash, 280, 281; pitted, 314, 407, 408.

Platform, continental, 18, 19; oceanic, 18, 19.

Playa lakes, 422.

Playfair, Sir John, cited, 178.

Plucking, beneath glaciers, 275.

Plugs, volcanic, 140.

Plunge and flow structure, 37.

Plunging folds, 43; detection of, 49, 50.

Pluvial periods, 198.

Pocket rocks, in desert, 200, 201, 202.

Poles, wind, of the earth, 263; earlier, 297.

_Poljen_, 189, 422.

Pompeii, destruction of, 97; volcanic materials over, 122.

_Ponores_, 188.

Porphyritic texture, of certain igneous rocks, 32.

Portals, in mountain rampart, surrounding continental glaciers, 271.

Potato shape, of earth, 7.

_Pourquoi-Pas_ expedition, 289.

Powell, J. W., cited, 178, 439, 446.

Pratt, W. E., cited, 147.

Precipitation, in relation to glaciation, 261.

Pressure ridges, on pack ice, 286.

Prinz, cited, 14, 19, 54, 133, 148.

Processes by which rocks are formed, 30.

Profile, cut by waves on steep rocky shore, 236.

Profiles, character, 177, 318; character, directly due to volcanic agencies, 145, 146; character, coast, due to uplift or depression, 259; character, of arid lands, 220; character, of shore features, 243; character, referable to mountain glaciers, 379; of cinder cones, 123.

Projectiles, lava, “bread-crust” type, 119; volcanic, 121.

Prying work of frost, 152.

“Pudding stone”, 463.

Pumiceous texture, of extrusive rocks, 32.

Pumpelly, Raphael, cited, 222.

Pumpelly, R. W., cited, 212.

_Puys_, 105.

_Puys_ of Auvergne, 124.

Pyrite, 452.

Pyrolusite, 456.

Pyroxenes, 458.

Quartz, 458.

Quartzite, 466.

_Quebradas_, 75.

Rabot, C., cited, 424.

Radiating glaciers, 383, 386.

Raft lakes, 417, 418.

Rafts, log, in Red River, 418.

Railway tracks, buckled, during earthquakes, 75.

Rain erosion, 214.

Rainfall, infrequent in deserts, 197.

Raised beaches, 326, 328.

Ramparts, ice, 431-434.

_Randspalte_, 370.

Rapids, in Rhine gorge, 169.

_Rapilli_, 122.

Rath, G. vom, cited, 147.

Reaction rims, about minerals, 28.

Receding hemicycle of glaciation, 264.

Recessional moraines, 399.

Reciprocal relation, of land and sea, map to show, 11.

Réclus, E., cited, 147.

Records, of rise or fall of land, 245.

Red clay, of the deep sea, 39.

Red color, of desert rocks, 202.

Reid, H. F., cited, 294, 296, 400.

Rejuvenated rivers, 173, 174.

Relief forms, carved by waves, 213.

Relief patterns, dividing lines of, 226.

Repeating patterns, in earth relief, 223; composite, 227.

Reservoirs, of lava, local, 95.

Residual rocks, 30.

Resistant rocks, in relation to erosion, 174.

Rhine, gorge of, 169.

Rhyolite, 463.

Ribbon falls, 378.

Richter, E., cited, 294.

Richtofen, Freiherr von, cited, 207, 222.

“Ridge roads”, 328.

_Riegel_, 377.

Rifting, in eroded mountains, 444.

Rift-valley lakes, 403, 404.

Rift valleys, 440.

Rigidity of the earth, 20, 29.

Ripple markings, 36.

River, zone of the dwindling, 213.

River capture, 175.

River deltas, 179.

River etchings, intricate pattern of, 158.

River lakes, 424.

River narrows, 174, 327.

River networks, in relation to precipitation, 161; in relation to rock architecture, 161; meshes of, 161.

Rivers, braided, 280; cross sections of, in successive stages, 172; drowned, 251, 340; early aspects of, 159; life begun in uplift, 159; life histories of, 158; motive power of, 158; rejuvenated, 173, 174; submerged channels of, 252; swollen during melting of continental glaciers, 320; tributary, accordant, 377; young, 159, 160.

River terraces, 165, 178.

River valley, longitudinal section of, 161.

_Roches moutonnées_, 276, 301, 367.

Rock bars, 377; cut through by gorges, 378.

Rock basin lakes, 376, 377, 400, 412.

Rock cleavage, 44.

“Rock glaciers”, 153.

“Rocking stones”, 306.

Rock mantle, 155; relation to topography, 156.

Rock pedestals, 381.

Rock terraces, 215.

Rocks, clastic, 30; corrosion of, 156; description of some common, 462-466; extrusive, 32, 463; igneous, 30; igneous, textures of, 32; igneous, massive structure of, 31; intrusive, 32, 462, 463; laminated structure of, 31; marks of origin of, 30; metamorphic, 30, 31, 465; residual, 30; sedimentary, 30; sedimentary, of chemical precipitation, 464; sedimentary, of mechanical origin, 463; sedimentary, of organic origin, 464; sedimentary, rounded grains of, 31; volcanic, 32.

Ross Barrier, 282.

Rudolph, E., cited, 92.

Rudski, M. P., cited, 19.

Russell, I. C., cited, 126, 147, 148, 175, 178, 222, 293, 294, 296, 381, 384, 414, 424, 425.

St. Anthony Falls, recession of, 327, 354.

St. David’s gorge, near Niagara, 352, 359, 360, 363.

St. Goars, on Rhine, 169.

Saint Martin, cited, 436.

St. Paul’s rocks, a dissected volcano, 141.

Salients, of newly incised upland, 169.

Salines, 423.

Salisbury, R. D., cited, 156, 160, 205, 222, 293, 295, 298, 300, 305, 313, 318, 319, 339, 424.

Salton sink, 420.

Sand, beach, 206; eolian, 206; volcanic, 122.

Sand blast, natural, 204.

Sand cones, 84.

“Sand devils”, 209.

Sandstone, 464.

Sand storms, 209.

Santa Catalina, 239, 257.

Sapper, K., cited, 111, 147, 148.

Sarasin, P. and F., cited, 248.

Sardeson, F. W., cited, 327, 339.

Saucer lakes, 415, 416.

Sawa Lake, of Persian desert, 199.

Scaling, 151.

Scape colks, 277.

Scars, from dissection of volcanoes, 142; meander, 165.

Schist, chlorite, 465; mica, 465; sericite, 465; talc, 465.

Schistosity, 31.

Schrader, cited, 436.

_Schratten_, 188.

Scidmore, E. R., cited, 70.

Scoriaceous texture, of extrusive rocks, 32.

Scott, I. D., cited, 411, 470.

Scott, R. F., cited, 282, 295.

Scott, W. B., cited, 6, 60, 72, 259, 274, 375.

“Scree”, 152.

Scrope, P., cited, 96, 124, 146.

Sea caves, 234; elevated, 248.

Sea coves, 233.

Sea ice, 286, 292.

Seaquakes, 69; distribution of, 70; downward movement of sea floor during, 81; number and magnitude of, 81.

Seasonal lakes, 189, 422.

Section, geological, 46, 47; across mountain wall about desert, 212.

Sederholm, J. J., cited, 315.

Sedimentary rocks, 30; of chemical precipitation, 464; of mechanical origin, 463; of organic origin, 464.

Seismic sea wave, 69; Japan, 1896, 70.

Seismotectonic lines, 87.

Sekiya, S., cited, 141, 148.

Séracs, 391.

Serapeum, at Pozzuoli, 254.

Sericite schist, 465.

Series, conformable, 51; unconformable, 51.

Serpentine, 460.

Shackleton, Sir Ernest, cited, 17, 282, 283, 292, 295.

Shadow erosion, 206.

Shadow weathering, 203.

Shale, 464.

Shaler, N. S., cited, 7, 157, 244, 306, 317, 319.

Shapes of rock folds, 43.

Shaw, E. W., cited, 425.

Shearing, in folds, 45.

“Sheep backs”, 276.

Shelf, continental, 18, 19.

Shelf ice, 281, 282, 283; Antarctic, 289, 290; of ice age, 317.

Sherzer, W. H., cited, 294.

Shields, of lithosphere, 436.

Shingle, 239.

Shoal water deposits, 36.

Shore current, work of, 237, 238.

Shore lines, elevated, 340; migration of landward with uplift, 251.

Side delta lakes, 418, 419.

Siderite, 456.

Sieberg, A., cited, 92.

Sieger, R., cited, 259.

Siliceous lava, viscous, 103.

Siliceous sinter, 194.

Sills, 142.

Sinclair, W. J., cited, 152.

Sink lakes, 421.

Sinks, in limestone, 182.

Sinter, calcareous, 184; siliceous, 194.

Sinter columns, formation of, 185.

Sinter deposits, 184.

Sjögren, Otto, cited, 225.

Skaptár fissure in Iceland, 99.

Skyline, straight, of mature upland, 170.

Slate, clay, 466.

Slichter, C. S., cited, 195.

Slickensides, on fault, 60.

Smith, George Otis, cited, 173.

Smithsonite, 456.

“Smoke” of volcanoes, nature of, 128.

Smyth, C. H., Jr., cited, 157.

Snake river, Idaho, lava plains of, 102.

Snickers Gap, 177.

Snow, B. W., cited, 193.

Snowbergs, 292, 293.

Snowdrift sites, 368.

Snow line, 261.

Soil flow, 153, 157.

Soil striping, 154.

Solfatara condition of volcanoes, 97.

Solger, F., cited, 222.

Solifluxion, 153, 157.

Sonklar, cited, 386.

Spallanzani, cited, 115.

Spatter cones, 104.

Speculative philosophy _vs._ observational geology, 5.

Spencer, J. W., cited, 260, 344, 350, 353, 366.

Spethmann, H., cited, 267.

Sphalerite, 453.

Spherulites, 33.

Spherulitic texture, of igneous rocks, 33.

Sphinx, erosion by natural sand blast, 205.

Spits, 240.

Spitzbergen, 154.

Springs, fissure, 190, 195; surface, 181; thermal, 190.

Stability, not the order of nature, 4.

Stacks, 233; elevated, 249, 343.

Stage of adolescence, 169, 170.

Stairway, cascade, 376.

Stalactites, growth of, 184.

Stalagmites, formation of, 185.

Staurolite, 460.

Steppes, 215.

Still river, of Connecticut, history of, 338.

Stone, G. H., cited, 253, 260, 315, 319.

“Stone ginger”, 208.

“Stone lattice”, 205, 206.

“Stone rivers”, 153.

Strahan, A., cited, 318.

Strand lakes, 424.

Strata, conformable, 51; contortions of, 40.

Straths, 428.

Streak, of minerals, 451.

Stream capture, 179.

Stream, meandering, cross section of, 163; braided, 280; intermittent, 180.

Stream velocity, determined by gradient, 158.

Strike, 46.

Striped ground, 154.

_Strokr_, 193.

Strombolian eruptions, 117.

Stromboli, cinder cone of, 115; excentric crater of, 115; explanation of eruptions in, 116, 117.

Structure, cross-bedded, 37.

Submerged channels, of rivers, 252.

Submergence of land, during earthquakes, 80.

Suess, E., cited, 19, 142, 259, 277, 425, 436, 437, 438, 446.

_Suffioni_, arrangement on faults, 87.

Supan, A., 420, 424.

Surface moraines, 277.

Surface springs, 181.

“Swallow holes”, 182, 422.

Swamp lands, drained during earthquakes, 83.

Sweinfurth, G., cited, 222.

Syenite, 462.

Symbols, T., to express strike and dip, 48.

Synclinal folds, 42.

Synclines, 42.

System of fractures, 55.

Taal volcano, double explosive eruption of 1911, 120, 121.

Table mountains, origin of, 112.

_Takyr_, 216.

Talc, 460.

Talc schist, 465.

Talmage, J. E., cited, 221.

Talus, 152, 153, 215.

Tangier-Smith, W. S., cited, 260.

Tarr, R. S., cited, 77, 92, 233, 260, 295, 301.

Taylor, F. B., cited, 259, 330, 339, 342, 343, 346, 350, 355, 366.

Tectonic lakes, 424.

Temperature, diurnal changes of, in deserts, 202.

Temple of Jupiter Serapis, oscillations of level of, 254, 255.

Terminal moraine, of Pleistocene glaciations, 298, 299.

Terminal moraines, of mountain glaciers, 394.

Terraced valleys, 320, 321.

Terraces, built, 235; coast, 80, 235, 341; river, 165, 178, 320, 321; rock, 215.

Terra Rossa, of Karst region, 188.

Tessellated pavement, from soil flow, 154.

Tethys, ocean of, 16.

Tetrahedron, reciprocal relations of antipodal parts, 13; truncated, toward which earth is tending, 12.

Tetrahedrons, twin, 16.

Thaw water, soil flow in presence of, 153.

Theory, evolved from working hypothesis, 6; mixture with observation, on maps, 63.

Thermal springs, 190.

Thickness of formations, 65.

Thompson, Bertha, cited, 155.

Thomson and Tait, cited, 29.

Thomson, Wyville, cited, 296.

Thoroddsen, Th., cited, 103, 123, 147, 267.

Throw, on faults, 59.

Thrusts, 45.

“Tidal waves”, 70.

Tides, effect on a fluid earth, 20.

Tidewater glaciers, 290, 386.

Till, 31, 310.

Tillite, 31.

Till plains, 311.

Tinds, 380, 381.

Tivoli, travertine of, 184.

Tombolas, 241.

Tongues, ice, on margin of continental glaciers, 272.

Topographic maps, 61; preparation of, 467.

Topography, built up, 301; constructional, 309; destructional, 309; fault, 65; fold, 65; incised, 301; knob and basin, 314.

Top-set beds, 167.

Tourmaline, 460.

Tower, W. S., cited, 178.

Trachyte, 463.

Transgression, of the sea, 37.

Transparency, of minerals, 451.

Travertine, 184, 464.

Trees, how affected by advancing lava, 133; undermined on stream meanders, 164.

“Trellis drainage”, 175.

Troughline, of a syncline, 42.

Trunk channels of descending water, 181.

Tsunamis, 70.

T symbols, to express strike and dip, 48.

Tufa, calcareous, 464.

Tunnels, lava, 111, 112, 125.

Twin tetrahedrons, 16.

Tyndall, John, cited, 192, 196.

Udden, J. A., cited, 222.

Unconformable series, 51.

Unconformity, 65; episodes in history of, 52; meaning of, 51.

Underfolding, of earth’s shell, 437.

Underground water, 180.

Undertow, 236.

Unstable erosion remnants, in “driftless area”, 300.

Upham, Warren, cited, 325, 327, 339, 344, 350.

Upland, fretted, 372, 373; grooved, 372, 373; maturely dissected, 170; mature, unfavorable to commercial development, 171; newly incised, 169; partially dissected, 160; progressive investment of, by cirques, 374.

Uplift, marks of, on coasts, 245; sudden, of coasts, 247.

Upraised cliffs, 249.

Uptilt, in basin of Lake Agassiz, 350; of glaciated area, evidence that it continues, 348-350; of glaciated area, supposed nature of, 344-347.

U-shaped valleys, 374.

Usu-san (New Mountain), birth of, 96.

Valley moraine lakes, 400, 413.

Valleys, hanging, 378; of V-form, 172; U-shaped, 374.

Valley trains, 311, 399.

Van Hise, C. R., cited, 54.

Varnish, desert, 201.

Veatch, A. C., cited, 418, 425.

Verbeek, R. D. M., cited, 100, 142, 147, 148.

Vesicular texture, of extrusive rocks, 32.

Victoria Falls, 225.

Vincentius of Beauvais, cited, 9.

Volcanic ash, 122.

“Volcanic bombs”, 121.

Volcanic dust, 122.

Volcanic eruptions, during changes in earth’s figure, 15.

Volcanic lakes, 424.

Volcanic mountains, of ejected materials, 115; of exudation, 94.

Volcanic necks, 140.

Volcanic pipes, 140.

Volcanic plugs, 139, 140.

Volcanic projectiles, 121.

Volcanic rocks, 32.

Volcanic sand, 122.

Volcano belts, of the earth, 98.

Volcano, definition of, 95.

Volcano, eruption in 1888, 118, 120, 147; history of, 118, 119.

Volcanoes, active, 97; arrangement over fissures, 99; birth of, 96; cone-producing period of, 127; convulsive eruptions of, 105; crater-producing period of, 128; dissection of, 139, 148; dormant, 97; early views concerning, 95; “elevation-crater” theory of, 95; explosive eruptions of, 105; extinct, 97; fissure eruptions of, 101; location at fissure intersections, 100; map of, in Java, 100; migration of vent along fissure, 101, 124; misconceptions concerning, 94; mud flows after eruptions, 138; of Gulf of Guinea, 101; regarded as retaining walls, 124, 125; relation to mountain ranges, 144; sequence of events within chimney of, during eruption, 134, 135; solfataric activity of, 97; three types of, 105.

V-shaped valley, 172.

Vulcanello, 119.

Vulcanian eruptions, 117, 125.

Waltershausen, S. von, cited, 148.

Walther, Johannes, cited, 201, 202, 203, 204, 205, 206, 211, 215, 221.

Wandering dunes, 209.

Warren river, 416.

“Washes”, 213.

Water, derangement of flow during earthquakes, 83; ground, 180; percolating, rôle of, 149; running, earth features shaped by, 169; shot up in sheets during earthquake, 83; thaw, soil flow in presence of, 153.

Water gaps, 176.

Water pipes, buckled in ground, during earthquakes, 75.

Water table, 180; extreme depth of, 201, 203.

Water wave, effect of breaking on shore, 233; free, 232; motion of, 231.

Watson, T. L., cited, 259.

Wave, water, the motion of, 231.

Wave base, 232.

Wave length, 231.

Weathering, carbonization, 151; chemical, 149; chemical agents of, 149; dry, 201; exfoliation, 151; frost action, 152; hydration, 151; in relation to climate, 150; internal, in deserts, 201; mechanical, 149; of lithosphere surface, 29; shadow, 203; spheroidal, 150, 151; two contrasted processes of, 149.

_Wed_ (_Wadi_), 212, 213, 214.

Weed, W. H., cited, 196, 441, 447.

West Indies, seismotectonic lines of, 88.

Wheeler, W. H., cited, 244.

Whirlpool basin, at Niagara, 359; excavation of, 360.

Whitbeck, R. H., cited, 319.

White, David, cited, 318.

Willis, Bailey, cited, 45, 54, 157, 260, 318.

Winchell, N. H., cited, 354.

Wind, in relation to location of glaciers, 377; in relation to mountain glaciers, 367.

Wind distribution of snow, 367.

Wind gaps, 176.

_Windkanten_, 205.

Wind poles, of the earth, 263; of earth, earlier, 297.

Wintergreen Flats, site of captured fall, 358.

Wisconsin diamonds, 307, 308.

Woodworth, J. B., cited, 74, 351.

Worcester, Dean C., cited, 96.

Working hypothesis, 6.

Workman, Fanny Bullock, cited, 294.

Workman, W. H., cited, 294.

Wright, F. E., cited, 351.

Yellowstone National Park, 33, 191, 193, 194.

Yosemite Valley, 59, 152.

Young rivers, 159, 160.

Zahn, G. W. von, cited, 244.

Zigzag ranges, due to plunging folds, 51.

Zittel, K. v., cited, 19.

Zone of diverse displacement, 439.

Zone of flow, 40, 143.

Zone of fracture, 40, 46.

Zones, of deposition, surrounding desert, 216, 217; upper and lower cloud, 268, 269.

Printed in the United States of America.

FOOTNOTES:

[1] Italian for mouth; plural _bocchi_.

[2] These models and the contouring apparatus are now manufactured for the use of schools and colleges by Eberbach and Son, Ann Arbor, Mich.

[3] This clay is manufactured by the A. H. Abbott Company, art dealers, Wabash Avenue, Chicago.

[4] Numbers in parenthesis refer to pages in this book, where further information is to be found.

* * * * * *

Transcriber’s note:

—Obvious typographical errors have been silently corrected. All other variations in spelling punctuation and accents have been left unchanged.

—A border has been added to plates.