CHAPTER VI.

The Lines of the Geographer rarely right Lines.--These last, however, always worth looking at when they occur.--Striking Instance in the Line of the Great Caledonian Valley.--Indicative of the Direction in which the Volcanic Agencies have operated.--Sections of the Old Red Sandstone furnished by the Granitic Eminences of the Line.--Illustration.--Lias of the Moray Frith.--Surmisings regarding its Original Extent.--These lead to an Exploratory Ramble.--Narrative.--Phenomena exhibited in the course of half an hour's Walk.--The little Bay.--Its Strata and their Organisms.

The natural boundaries of the geographer are rarely described by right lines. Whenever these occur, however, the geologist may look for something remarkable. There is one very striking example furnished by the north of Scotland. The reader, in consulting a map of the kingdom, will find that the edge of a ruler, laid athwart the country in a direction from south-west to north-east, touches the whole northern side of the great Caledonian Valley, with its long, straight line of lakes; and onwards, beyond the valley's termination at both ends, the whole northern side of Loch Eil and Loch Linnhe, and the whole of the abrupt and precipitous northern shores of the Moray Frith, to the extreme point of Tarbat Ness--a right line of considerably more than a hundred miles. Nor does the geography of the globe furnish a line better defined by natural marks. There is both rampart and fosse. On the one hand we have the rectilinear lochs and lakes, with an average profundity of depth more than equal to that of the German Ocean, and, added to these, the rectilinear lines of frith; on the other hand, with but few interruptions, there is an inclined wall of rock, which rises at a steep angle in the interior to nearly two thousand feet over the level of the Great Canal, and overhangs the sea towards its northern termination, in precipices of more than a hundred yards.[AF]

[Footnote AF: The valley of the Jordan, from the village of Laish to the southern extremity of the Dead Sea, furnishes another very remarkable instance of a geographical right line.]

The direction of this rampart and fosse--this Roman wall of Scottish geological history--seems to have been that in which the volcanic agencies chiefly operated in upheaving the entire island from the abyss. The line survives as a sort of foot-track, hollowed by the frequent tread of earthquakes, to mark the course in which they journeyed. Like one of the great lines in a trigonometrical survey, it enables us, too, to describe the lesser lines, and to determine their average bearing. _The volcanic agencies must have extended athwart the country from south-west to north-east._ Mark in a map of the island--all the better if it be a geological one--the line in which most of our mountain ranges stretch across from the German Ocean to the Atlantic,--the line, too, in which our friths, lochs, and bays, on both the eastern and western coasts, and especially those of the latter, run into the interior. Mark, also, the line of the geological formations, where least broken by insulated groups of hills--the line, for instance, of the Old Red Sandstone belt, which flanks the southern base of the Grampians--the nearly parallel line of our Scottish Coal-field, in its course from sea to sea--the line of the Grauwacke, which forms so large a portion of the south of Scotland--the line of the English Coal-field, of the Lias, of the Oolite, of the Chalk--and how in this process of diagonal lining, if I may so speak, the south-eastern portion of England comes to be cut off from the secondary formations altogether, and, but for the denudation of the valley of the Weald, would have exhibited only tertiary depositions. In all these lines, whether of mountains, lakes, friths, or formations, there is an approximation to parallelism with the line of the great Caledonian valley--proofs that the upheaving agency from beneath must have acted in this direction from some unknown cause, during all the immensely extended term of its operations, and along the entire length of the island. It is a fact not unworthy of remark, that the profound depths of Loch Ness undulated in strange sympathy with the reeling towers and crashing walls of Lisbon, during the great earthquake of 1755; and that the impulse, true to its ancient direction, sent the waves in huge furrows to the north-east and the south-west.

The north-eastern portion of this rectilinear wall or chain runs, for about thirty miles, through an Old Red Sandstone district. The materials which compose it are as unlike those of the plain out of which it arises, as the materials of a stone dike, running half-way into a field, are unlike the vegetable mould which forms the field's surface. The ridge itself is of a granitic texture--a true gneiss. At its base we find only conglomerates, sandstones, shales, and stratified clays, and these lying against it in very high angles. Hence the geological interest of this lower portion of the wall. As has been shrewdly remarked by Mr. Murchison,[AG] in one of his earlier papers, the gneiss seems to have been forced through the sandstone from beneath, in a solid, not a fluid form; and as the ridge a-top is a narrow one, and the sides remarkably abrupt--an excellent wedge, both in consistency and form--instead of having acted on the surrounding depositions, as most of the south country traps have done that have merely issued from a vent, and overlaid the upper strata, it has torn up the entire formation from the very bottom. Imagine a large wedge forced from below through a sheet of thick ice on a river or pond. First the ice rises in an angle, that becomes sharper and higher as the wedge rises; then it cracks and opens, presenting its upturned edges on both sides, and through comes the wedge. And this is a very different process, be it observed, from what takes place when the ice merely cracks, and the water issues through the crack. In the one case there is a rent, and water diffused over the surface; in the other, there is the projecting wedge, flanked by the upturned edges of the ice; and these edges, of course, serve as indices to decide regarding the ice's thickness, and the various layers of which it is composed. Now, such are the phenomena exhibited by the wedge-like granitic ridge. The Lower Old Red Sandstone, tilted up against it on both sides, at an angle of about eighty, exhibits in some parts a section of well nigh two thousand feet, stretching from the lower conglomerate to the soft, unfossiliferous sandstone, which forms in Ross and Cromarty the upper beds of the formation. There is a mighty advantage to the geologist in this arrangement. When books are packed up in a deep box or chest, we have to raise the upper tier ere we can see the tier below, and this second tier ere we can arrive at a third, and so on to the bottom. But when well arranged on the shelves of a library, we have merely to run the eye along their lettered backs, and we can thus form an acquaintance with them at a glance, which in the other case would have cost us a good deal of trouble. Now, in the neighborhood of this granitic wedge, or wall, the strata are arranged, not like books in a box,--such was their original position,--but like books on the shelves of a library. They have been unpacked and arranged by the uptilting agent; and the knowledge of them, which could only have been attained in their first circumstances by perforating them with a shaft of immense depth, may now be acquired simply by passing over their edges. A morning's saunter gives us what would have cost, but for the upheaving granite, the labor of a hundred miners for five years.

[Footnote AG: See _Transactions of the London Geological Society_ for 1828, p. 354.]

By far the greater portion of the life of the writer was spent within less than half an hour's walk of one of these upturned edges. I have described the granitic rock, with reference to the disturbance it has occasioned as a wedge forced from below, and with reference to its rectilinear position in the sandstone district which it traverses, as a stone wall running half-way into a field. It may communicate a still corrector and livelier idea to think of it as a row of wedges, such as one sometimes sees in a quarry when the workmen are engaged in cutting out from the mass some immense block, intended to form a stately column or huge architrave. The eminences, like the wedges, are separated; in some places the sandstone lies between--in others there occur huge chasms filled by the sea. The Friths of Cromarty and Beauly, for instance, and the Bay of Munlochy, open into the interior between these wedge-like eminences;--the well-known Sutors of Cromarty represent two of the wedges; and it was the section furnished by the Southern Sutor that lay so immediately in the writer's neighborhood. The line of the Cromarty Frith forms an angle of about thirty-five degrees with that of the granitic line of wedge-like hills which it bisects; and hence the peculiar shape of that tongue of land which forms the lower portion of the Black Isle, and which, washed by the Moray Frith on the one side, and by the Frith of Cromarty on the other, has its apex occupied by the Southern Sutor. Imagine a lofty promontory somewhat resembling a huge spear thrust horizontally into the sea--a ponderous mass of granitic gneiss, of about a mile in length, forming the head, and a rectilinear line of the Old Red Sandstone, more than ten miles in length, forming the shaft; and such is the appearance which this tongue of land presents, when viewed from its north-western boundary, the Cromarty Frith. When viewed from the Moray Frith,--its south-western boundary,--we see the same granitic spear-head, but find the line of the shaft knobbed by the other granitic eminences of the chain.

Now on this tongue of land I first broke ground as a geologist. The quarry described in my introductory chapter, as that in which my notice was first attracted by the ripple markings, opens on the Cromarty Frith side of this huge spear-shaft; the quarry to which I removed immediately after, and beside which I found the fossils of the Lias, opens on its Moray Frith side. The uptilted section of sandstone occurs on both sides, where the shaft joins to the granitic spear-head, but the Lias I found on the Moray Frith side alone. It studs the coast in detached patches, sorely worn by the incessant lashings of the Frith; and each patch bears an evident relation, in the place it occupies, to a corresponding knob or wedge in the granitic line. The Northern Sutor, as has been just said, is one of these knobs or wedges. It has its accompanying patch of Lias upheaved at its base, and lying unconformably, not only to its granitic strata, but also to its subordinate sandstones. The Southern Sutor, another of these knobs, has also its accompanying patch of Lias, which, though lying beyond the fall of the tide, strews the beach, after every storm from the east, with its shales and its fossils. The hill of Eathie is yet another knob of the series, and it, too, has its Lias patch. The granitic wedges have not only uptilted the sandstone, but they have also upheaved the superincumbent Lias, which, but for their agency, would have remained buried under the waters of the Frith, and its ever accumulating banks of sand and gravel. I had remarked at an early period the correspondence of the granitic knobs with the Lias patches, and striven to realize the original place and position of the latter ere the disturbing agent had upcast them to the light. What, I have asked, was the extent of this comparatively modern formation in this part of the world, ere the line of wedges were forced through from below? A wedge struck through the ice of a pond towards the centre breaks its continuity, and we find the ice on both sides the wedge; whereas, when struck through at the pond edge, it merely raises the ice from the bank, and we find it, in consequence, on but one side the wedge. Whether, have I often inquired, w T ere the granitic wedges of this line forced through the Lias at one of its edges, or at a comparatively central point? and about ten years ago I set myself to ascertain whether I could not solve the question. The Southern Sutor is a wedge open to examination on both its sides;--the Moray Frith washes it upon one side, the Cromarty Frith on the other. Was the Lias to be found on both its sides? If so, the wedge must have been forced _through_ the formation, not merely _beside_ it. It occurs, as I have said, on the Moray Frith side of the wedge; and I resolved, on carefully exploring the Frith of Cromarty, to try whether it did not occur on that side too.

With this object I set out on an exploratory excursion, on a delightful morning of August, 1830. The tide was falling; it had already reached the line of half ebb; and from the Southern Sutor to the low, long promontory on which the town of Cromarty is built, there extended a broad belt of mingled sand-banks and pools, accumulations of boulders, and shingle, and large tracts darkened with algæ. I passed direct by a grassy pathway to the Sutor, the granitic spear-head of a late illustration,--and turned, when I reached the curved and contorted gneiss, to trace through the broad belt left by the retiring waters, and in a line parallel to what I have described as the shaft of the huge spear, the beds and strata of the Old Red Sandstone in their ascending succession. I first crossed the conglomerate base of the system, here little more than a hundred feet in thickness. The ceaseless dash of the waves, which smooth most other rocks, has a contrary effect on this bed, except in a few localities, where its arenaceous cement of base is much indurated. Under both the Northern and Southern Sutors the softer cement yields to the incessant action, while the harder pebbles stand out in bold relief; so that, wherever it presents a mural front to the breakers, we are reminded, by its appearance, of the artificial rock work of the architect. It roughens as the rocks around it polish. Quitting the conglomerate, I next passed over a thick bed of coarse reel and yellow sandstone, with here and there a few pebbles sticking from its surface, and here and there a stratum of finer-grained fissile sandstone inserted between the rougher strata: I then crossed over a strata of an impure grayish limestone, and a slaty clay, abounding, as I long afterwards ascertained, in ichthyolites and vegetable remains. There are minute veins in the limestone (apparently cracks filled up) of a jet black bituminous substance, resembling anthracite; the stratified clay is mottled by layers of semi-aluminous, semi-calcareous nodules, arranged like layers of flint in the upper Chalk. These nodules, when cut up and polished, present very agreeable combinations of color; there is generally an outer ring of reddish brown, an inner ring of pale yellow, and a central patch of red, and the whole is prettily veined with dark-colored carbonate of lime.[AH] Passing onwards and upwards in the line of the strata, I next crossed over a series of alternate beds of coarse sandstone and stratified clay, and then lost sight of the rock altogether, in a wide waste of shingle and boulder-stones, resting on a dark blue argillaceous diluvium, sometimes employed in that part of the country, from its tenacious and impermeable character, for lining ponds and dams, and as mortar for the foundations of low-lying houses, exposed in wet weather to the sudden rise of water. The numerous boulders of this tract have their story to tell, and it is a curious one. The Southern Sutor, with its multitudinous fragments of gneiss, torn from its sides by the sea, or loosened by the action of frosts and storms, and rolled down its precipices, is only a few hundred yards away;--its base, where these lie thickest, has been swept by tempests, chiefly from the east, for thousands and thousands of years; and the direct effect of these tempests, regarded as transporting agents, would have been to strew this stony tract with those detached fragments. The same billow that sends its long roll from the German Ocean to sweep the base of the Sutor, and to leap up against its precipices to the height of eighty and a hundred feet, breaks in foam, only a minute after, over this stony tract; which has, in consequence, its sprinkling of fragments of gneiss, transported by an agency so obvious. But for every one such fragment which it bears, we find at least ten boulders that have been borne for forty and fifty miles in the opposite direction from the interior of the country--a direction in which no transporting agency now exists. The tempests of thousands of years have conveyed for but a few hundred yards not more than a tithe of the materials of this tract; nine tenths of the whole have been conveyed by an older agency over spaces of forty and fifty miles. How immensely more powerful, then, or how immensely protracted in its operation, must that older agency have been!

[Footnote AH: A concretionary limestone of the Old Red system in England, variegated with purple and green, was at one time wrought as a marble.--_Silurian System_, Part i. p. 176.]

I passed onwards, and reached a little bay, or, rather, angular indentation of the coast, in the neighborhood of the town. It was laid bare by the tide, this morning, far beyond its outer opening; and the huge, table-like boulder, which occupies nearly its centre, and to which, in a former chapter, I have had occasion to refer, held but a middle place between the still darkened flood-line that ran high along the beach, and the brown line of ebb that bristled far below with forests of the rough-stemmed tangle. This little bay, or inflection of the coast, serves as a sort of natural wear in detaining floating drift-weed, and is often found piled, after violent storms from the east, with accumulations, many yards in extent, and several feet in depth, of kelp and tangle, mixed with zoöphytes and mollusca, and the remains of fish killed among the shallows by the tempest. Early in the last century, a large body of herrings, pursued by whales and porpoises, were stranded in it, to the amount of several hundred barrels; and it is said that salt and cask failed the packers when but comparatively a small portion of the shoal were cured, and that by much the greatest part of them were carried away by the neighboring farmers for manure. Ever since the formation of the present coast-line, this natural wear has been arresting, tide after tide, its heaps of organic matter, but the circumstances favorable to their preservation have been wanting: they ferment and decay when driven high on the beach; and the next spring-tide, accompanied by a gale from the west, sweeps every vestige of them away; and so, after the lapse of many centuries, we find no other organisms among the rounded pebbles that form the beach of this little bay, than merely a few broken shells, and occasionally a mouldering fish-bone. Thus very barren formations may belong to periods singularly rich in organic existences. When what is now the little bay was the bottom of a profound ocean, and far from any shore, the circumstances for the preservation of its organisms must have been much more favorable. In no locality in the Old Red Sandstone with which I am acquainted have such beautifully preserved fossils been found. But I anticipate.

In the middle of the little bay, and throughout the greater part of its area, I found the rock exposed--a circumstance which I had marked many years before, when a mere boy, without afterwards recurring to it as one of interest. But I had now learned to look at rocks with another eye; and the thought which first suggested itself to me regarding the rock of the little bay was, that I had found the especial object of my search--the Lias. The appearances are in some respects not dissimilar. The Lias of the north of Scotland is represented in some localities by dark-colored, unctuous clays, in others by grayish black sandstones, that look like indurated mud, and in others by beds of black fissile shale, alternating with bands of coarse, impure limestone, and studded between the bands with limestone nodules of richer quality and finer grain. The rock laid bare in the little bay is a stratified clay, of a gray color tinged with olive, and occurring in beds separated by indurated bands of gray, micaceous sandstone. They also abound in calcareous nodules. The dip of the strata, too, is very different from that of the beds which lean against the gneiss of the Sutor. Instead of an angle of eighty, it presents an angle of less than eight. The rocks of the little bay must have lain beyond the disturbing, uptilting influence of the granitic wedge. So thickly are the nodules spread over the surface of some of the beds, that they reminded me of floats of broken ice on the windward side of a lake after a few days' thaw, when the edges of the fragments are smoothed and rounded, and they press upon one another, so as to cover, except in the angular interstices, the entire surface.

I set myself carefully to examine. The first nodule I laid open contained a bituminous looking mass, in which I could trace a few pointed bones and a few minute scales. The next abounded in rhomboidal and finely enamelled scales, of much larger size and more distinct character. I wrought on with the eagerness of a discoverer entering for the first time in a _terra incognita_ of wonders. Almost every fragment of clay, every splinter of sandstone, every limestone nodule, contained its organism--scales, spines, plates, bones, entire fish; but not one organism of the Lias could I find--no ammonites, no belemnites, no gryphites, no shells of any kind: the vegetable impressions were entirely different; and not a single scale, plate, or ichthyodorulite could I identify with those of the newer formation. I had got into a different world, and among the remains of a different creation; but where was its proper place in the scale? The beds of the little bay are encircled by thick accumulations of diluvium and debris, nor could I trace their relation to a single known rock. I was struck, as I well might, by the utter strangeness of the forms--the oar-like arms of the _Pterichthys_ and its tortoise-like plates--the strange, buckler-looking head of the _Coccosteus_, which, I suppose, might possibly be the back of a small tortoise, though the tubercles reminded me rather of the skin of the shark--the polished scales and plates of the _Osteolepis_--the spined and scaled fins of the _Cheiracanthus_--above all, the one-sided tail of at least eight out of the ten or twelve varieties of fossil which the deposit contained. All together excited and astonished me. But some time elapsed ere I learned to distinguish the nicer generic differences of the various organisms of the formation. I found fragments of the _Pterichthys_ on this morning; but I date its discovery, in relation to the mind of the discoverer, more than a twelvemonth later.[AI] I confounded the _Cheiracanthus_, too, with its single-spined, membranous dorsal, with _Diplacanthus_ ichthyolite, furnished with two such dorsals; and the _Diplopterus_ with the _Osteolepis_. Still, however, I saw enough to exhilarate and interest: I wrought on till the advancing tide came splashing over the nodules, and a powerful August sun had risen towards the middle sky; and were I to sum up all my happier hours, the hour would not be forgotten in which I sat down on a rounded boulder of granite, by the edge of the sea, when the last bed was covered, and spread out on the beach before me the spoils of the morning.

[Footnote AI: I find, by some notes, which had escaped my notice when drawing up for the _Witness_ newspaper the sketches now expanded into a volume, that in the year 1834 I furnished the collection of a geological friend, the Rev. John Swanson, minister of the parish of Small Isles, in the Outer Hebrides, with a well-marked specimen of the _Pterichthys Milleri_. The circumstance pleasingly reminds me of the first of all my early acquaintance, who learned to deem the time not idly squandered that was spent in exploring the wonders of bygone creations. Does the minister of Small Isles still remember the boy who led him in quest of petrifactions--himself a little boy at the time--to a deep, solitary cave on the Moray Frith, where they lingered amidst stalactites and mosses till the wild sea had surrounded them unmarked, barring all chance of retreat, and the dark night came on?]