Part 15

In the great eruption of Vesuvius, in August 1779, which Sir William Hamilton witnessed from his villa at Pausilippo in the bay of Naples, the volcano sent up white sulphureous smoke resembling bales of cotton, exceeding the height and size of the mountain itself at least four times; and in the midst of this vast pile of smoke, stones, scoriæ, and ashes were thrown up not less than 2000 feet. Next day a fountain of fire shot up with such height and brilliancy that the smallest objects could be clearly distinguished at any place within six miles or more of Vesuvius. But on the following day a more stupendous column of fire rose three times the height of Vesuvius (3700 feet), or more than two miles high. Among the huge fragments of lava thrown out during this eruption was a block 108 feet in circumference and 17 feet high, another block 66 feet in circumference and 19 feet high, and another 16 feet high and 92 feet in circumference, besides thousands of smaller fragments. Sir William Hamilton suggests that from a scene of the above kind the ancient poets took their ideas of the giants waging war with Jupiter.

The eruption of June 1794, which destroyed the greater part of the town of Torre del Greco, was, however, the most violent that has been recorded after the two great eruptions of 79 and 1631.

EARTH-WAVES.

The waves of an earthquake have been represented in their progress, and their propagation, through rocks of different density and elasticity; and the causes of the rapidity of propagation, and its diminution by the refraction, reflection, and interference of the oscillations have been mathematically investigated. Air, water, and earth waves follow the same laws which are recognised by the theory of motion, at all events in space; but the earth-waves are accompanied in their destructive action by discharges of elastic vapours, and of gases, and mixtures of pyroxene crystals, carbon, and infusorial animalcules with silicious shields. The more terrific effects are, however, when the earth-waves are accompanied by cleavage; and, as in the earthquake of Riobamba, when fissures alternately opened and closed again, so that men saved themselves by extending both arms, in order to prevent their sinking.

As a remarkable example of the closing of a fissure, Humboldt mentions that, during the celebrated earthquake in 1851, in the Neapolitan province of Basilicata, a hen was found caught by both feet in the street-pavement of Barile, near Melfi.

Mr. Hopkins has very correctly shown theoretically that the fissures produced by earthquakes are very instructive as regards the formation of veins and the phenomenon of dislocation, the more recent vein displacing the older formation.

RUMBLINGS OF EARTHQUAKES.

When the great earthquake of Coseguina, in Nicaragua, took place, January 23, 1835, the subterranean noise--the sonorous waves in the earth--was heard at the same time on the island of Jamaica and on the plateau of Bogota, 8740 feet above the sea, at a greater distance than from Algiers to London. In the eruptions of the volcano on the island of St. Vincent, April 30, 1812, at 2 A.M., a noise like the report of cannons was heard, without any sensible concussion of the earth, over a space of 160,000 geographical square miles. There have also been heard subterranean thunderings for two years without earthquakes.

HOW TO MEASURE AN EARTHQUAKE-SHOCK.

A new instrument (the Seismometer) invented for this purpose by M. Kreil, of Vienna, consists of a pendulum oscillating in every direction, but unable to turn round on its point of suspension; and bearing at its extremity a cylinder, which, by means of mechanism within it, turns on its vertical axis once in twenty-four hours. Next to the pendulum stands a rod bearing a narrow elastic arm, which slightly presses the extremity of a lead-pencil against the surface of the cylinder. As long as the pendulum is quiet, the pencil traces an uninterrupted line on the surface of the cylinder; but as soon as it oscillates, this line becomes interrupted and irregular, and these irregularities indicate the time of the commencement of an earthquake, together with its duration and intensity.[30]

Elastic fluids are doubtless the cause of the slight and perfectly harmless trembling of the earth’s surface, which has often continued for several days. The focus of this destructive agent, the seat of the moving force, lies far below the earth’s surface; but we know as little of the extent of this depth as we know of the chemical nature of these vapours that are so highly compressed. At the edges of two craters,--Vesuvius and the towering rock which projects beyond the great abyss of Pichincha, near Quito,--Humboldt has felt periodic and very regular shocks of earthquakes, on each occasion from twenty to thirty seconds before the burning scoriæ or gases were erupted. The intensity of the shocks was increased in proportion to the time intervening between them, and consequently to the length of time in which the vapours were accumulating. This simple fact, which has been attested by the evidence of so many travellers, furnishes us with a general solution of the phenomenon, in showing that active volcanoes are to be considered as safety-valves for the immediate neighbourhood. There are instances in which the earth has been shaken for many successive days in the chain of the Andes, in South America. In certain districts, the inhabitants take no more notice of the number of earthquakes than we in Europe take of showers of rain; yet in such a district Bonpland and Humboldt were compelled to dismount, from the restiveness of their mules, because the earth shook in a forest for fifteen to eighteen minutes _without intermission_.

EARTHQUAKES AND THE MOON.

From a careful discussion of several thousand earthquakes which have been recorded between 1801 and 1850, and a comparison of the periods at which they occurred with the position of the moon in relation to the earth, M. Perry, of Dijon, infers that earthquakes may possibly be the result of attraction exerted by that body on the supposed fluid centre of our globe, somewhat similar to that which she exercises on the waters of the ocean; and the Committee of the Institute of France have reported favourably upon this theory.

THE GREAT EARTHQUAKE OF LISBON.

The eloquent Humboldt remarks, that the activity of an igneous mountain, however terrific and picturesque the spectacle may be which it presents to our contemplation, is always limited to a very small space. It is far otherwise with earthquakes, which, although scarcely perceptible to the eye, nevertheless simultaneously propagate their waves to a distance of many thousand miles. The great earthquake which destroyed the city of Lisbon, November 1st, 1755, was felt in the Alps, on the coast of Sweden, into the Antilles, Antigua, Barbadoes, and Martinique; in the great Canadian lakes, in Thuringia, in the flat country of northern Germany, and in the small inland lakes on the shores of the Baltic. Remote springs were interrupted in their flow,--a phenomenon attending earthquakes which had been noticed among the ancients by Demetrius the Callatian. The hot springs of Töplitz dried up and returned, inundating every thing around, and having their waters coloured with iron ochre. At Cadiz, the sea rose to an elevation of sixty-four feet; while in the Antilles, where the tide usually rises only from twenty-six to twenty-eight inches, it suddenly rose about twenty feet, the water being of an inky blackness. It has been computed that, on November 1st, 1755, a portion of the earth’s surface four times greater than that of Europe was simultaneously shaken.[31] As yet there is no manifestation of force known to us (says the vivid denunciation of the philosopher), including even the murderous invention of our own race, by which a greater number of people have been killed in the short space of a few minutes: 60,000 were destroyed in Sicily in 1693, from 30,000 to 40,000 in the earthquake of Riobamba in 1797, and probably five times as many in Asia Minor and Syria under Tiberius and Justinian the elder, about the years 19 and 526.

GEOLOGICAL AGE OF THE DIAMOND.

The discovery of Diamonds in Russia, far from the tropical zone, has excited much interest among geologists. In the detritus on the banks of the Adolfskoi, no fewer than forty diamonds have been found in the gold alluvium, only twenty feet above the stratum in which the remains of mammoths and rhinoceroses are found. Hence Humboldt has concluded that the formation of gold-veins, and consequently of diamonds, is comparatively of recent date, and scarcely anterior to the destruction of the mammoths. Sir Roderick Murchison and M. Verneuil have been led to the same result by different arguments.[32]

WHAT WAS ADAMANT?

Professor Tennant replies, that the Adamant described by Pliny was a sapphire, as proved by its form, and by the fact that when struck on an anvil by a hammer it would make an indentation in the metal. A true diamond, under such circumstances, would fly into a thousand pieces.

WHAT IS COAL?

The whole evidence we possess as to the nature of Coal proves it to have been originally a mass of vegetable matter. Its microscopical characters point to its having been formed on the spot in which we find it, to its being composed of vegetable tissues of various kinds, separated and changed by maceration, pressure, and chemical action, and to the introduction of its earthy matter, in a large number of instances, in a state of solution or fine molecular subdivision. Dr. Redfern, from whose communication to the British Association we quote, knows nothing to countenance the supposition that our coal-beds are mainly formed of coniferous wood, because the structures found in mother-coal, or the charcoal layer, have not the character of the glandular tissue of such wood, as has been asserted.

Geological research has shown that the immense forests from which our coal is formed teemed with life. A frog as large as an ox existed in the swamps, and the existence of insects proves that the higher order of organic creation flourished at this epoch.

It has been calculated that the available coal-beds in Lancashire amount in weight to the enormous sum of 8,400,000,000 tons. The total annual consumption of this coal, it has been estimated, amounts to 3,400,120 tons; hence it is inferred that the coal-beds of Lancashire, at the present rate of consumption, will last 2470 years. Making similar calculations for the coal-fields of South Wales, the north of England, and Scotland, it will readily be perceived how ridiculous were the forebodings which lecturing geologists delighted to indulge in a few years ago.

TORBANE-HILL COAL.

The coal of Torbane Hill, Scotland, is so highly inflammable, that it has been disputed at law whether it be true coal, or only asphaltum, or bitumen. Dr. Redfern describes it as laminated, splitting with great ease horizontally, like many cannel coals, and like them it may be lighted at a candle. In all parts of the bed stigmaria and other fossil plants occur in greater numbers than in most other coals; their distinct vascular tissue may be easily recognised by a common pocket lens, and 65½ of the mass consists of carbon.

Dr. Redfern considers that all our coals may be arranged in a scale having the Torbane-Hill coal at the top and anthracite at the bottom. Anthracite is almost pure carbon; Torbane Hill contains less fixed carbon than most other cannels: anthracite is very difficult to ignite, and gives out scarcely any gas; Torbane-Hill burns like a candle, and yields 3000 cubic feet of gas per ton, more than any other known coal, its gas being also of greatly superior illuminating power to any other. The only differences which the Torbane-Hill coal presents from others are differences of degree, not of kind. It differs from other coals in being the best gas-coal, and from other cannels in being the best cannel.

HOW MALACHITE IS FORMED.

The rich copper-ore of the Ural, which occurs in veins or masses, amid metamorphic strata associated with igneous rocks, and even in the hollows between the eruptive rocks, is worked in shafts. At the bottom of one of these, 280 feet deep, has been found an enormous irregularly-shaped botryoidal mass of _Malachite_ (Greek _malache_, mountain-green), sending off strings of green copper-ore. The upper surface of it is about 18 feet long and 9 wide; and it was estimated to contain 15,000 poods, or half a million pounds, of pure and compact malachite. Sir Roderick Murchison is of opinion that this wonderful subterraneous incrustation has been produced in the stalagmitic form, during a series of ages, by copper solutions emanating from the surrounding loose and sporous mass, and trickling through it to the lowest cavity upon the subjacent solid rock. Malachite is brought chiefly from one mine in Siberia; its value as raw material is nearly one-fourth that of the same weight of pure silver, or in a manufactured state three guineas per pound avoirdupois.[33]

LUMPS OF GOLD IN SIBERIA.

The gold mines south of Miask are chiefly remarkable for the large lumps or _pepites_ of gold which are found around the Zavod of Zarevo-Alexandroisk. Previous to 1841 were discovered here lumps of native gold; in that year a lump of twenty-four pounds was met with; and in 1843 a lump weighing about seventy-eight pounds English was found, and is now deposited with others in the Museum of the Imperial School of Mines at St. Petersburg.

SIR ISAAC NEWTON UPON BURNET’S THEORY OF THE EARTH.

In 1668, Dr. Thomas Burnet printed his _Theoria Telluris Sacra_, “an eloquent physico-theological romance,” says Sir David Brewster, “which was to a certain extent adopted even by Newton, Burnet’s friend. Abandoning, as some of the fathers had done, the hexaëmeron, or six days of Moses, as a physical reality, and having no knowledge of geological phenomena, he gives loose reins to his imagination, combining passages of Scripture with those of ancient authors, and presumptuously describing the future catastrophes to which the earth is to be exposed.” Previous to its publication, Burnet presented a copy of his book to Newton, and requested his opinion of the theory which it propounded. Newton took “exceptions to particular passages,” and a correspondence ensued. In one of Newton’s letters he treats of the formation of the earth, and the other planets, out of a general chaos of the figure assumed by the earth,--of the length of the primitive days,--of the formation of hills and seas, and of the creation of the two ruling lights as the result of the clearing up of the atmosphere. He considers the account of the creation in Genesis as adapted to the judgment of the vulgar. “Had Moses,” he says, “described the processes of creation as distinctly as they were in themselves, he would have made the narrative tedious and confused amongst the vulgar, and become a philosopher more than a prophet.” After referring to several “causes of meteors, such as the breaking out of vapours from below, before the earth was well hardened, the settling and shrinking of the whole globe after the upper regions or surface began to be hard,” Newton closes his letter with an apology for being tedious, which, he says, “he has the more reason to do, as he has not set down any thing he has well considered, or will undertake to defend.”--See the Letter in the Appendix to _Sir D. Brewster’s Life of Newton_, vol. ii.

The primitive condition of the earth, and its preparation for man, was a subject of general speculation at the close of the seventeenth century. Leibnitz, like his great rival (Newton), attempted to explain the formation of the earth, and of the different substances which composed it; and he had the advantage of possessing some knowledge of geological phenomena: the earth he regarded as having been originally a burning mass, whose temperature gradually diminished till the vapours were condensed into a universal ocean, which covered the highest mountains, and gradually flowed into vacuities and subterranean cavities produced by the consolidation of the earth’s crust. He regarded fossils as the real remains of plants and animals which had been buried in the strata; and, in speculating on the formation of mineral substances, he speaks of crystals as the geometry of inanimate nature.--_Brewster’s Life of Newton_, vol. ii. p. 100, note. (See also “The Age of the Globe,” in _Things not generally Known_, p. 13.)

“THE FATHER OF ENGLISH GEOLOGY.”

In 1769 was born, the son of a yeoman of Oxfordshire, William Smith. When a boy he delighted to wander in the fields, collecting “pound-stones” (_Echinites_), “pundibs” (_Terebratulæ_), and other stony curiosities; and receiving little education beyond what he taught himself, he learned nothing of classics but the name. Grown to be a man, he became a land-surveyor and civil engineer, and was much engaged in constructing canals. While thus occupied, he observed that all the rocky masses forming the substrata of the country were gently inclined to the east and south-east,--that the red sandstones and marls above the _coal-measures_ passed below the beds provincially termed lias-clay and limestone--that these again passed underneath the sands, yellow limestone, and clays that form the table-land of the Coteswold Hills; while they in turn plunged beneath the great escarpment of chalk that runs from the coast of Dorsetshire northward to the Yorkshire shores of the German Ocean. He further observed that each formation of clay, sand, or limestone, held to a very great extent its own peculiar suite of fossils. The “snake-stones” (_Ammonites_) of the lias were different in form and ornament from those of the inferior oolite; and the shells of the latter, again, differed from those of the Oxford clay, Cornbrash, and Kimmeridge clay. Pondering much on these things, he came to the then unheard-of conclusion that each formation had been in its turn a sea-bottom, in the sediments of which lived and died marine animals now extinct, many specially distinctive of their own epochs in time.

Here indeed was a discovery,--made, too, by a man utterly unknown to the scientific world, and having no pretension to scientific lore. “Strata Smith’s” find was unheeded for many a long year; but at length the first geologists of the day learned from the land-surveyor that superposition of strata is inseparably connected with the succession of life in time. Hooke’s grand vision was at length realised, and it was indeed possible “to build up a terrestrial chronology from rotten shells” imbedded in the rocks. Meanwhile he had constructed the first geological map of England, which has served as a basis for geological maps of all other parts of the world. William Smith was now presented by the Geological Society with the Wollaston Medal, and hailed as “the Father of English Geology.” He died in 1840. Till the manner as well as the fact of the first appearance of successive forms of life shall be solved, it is not easy to surmise how any discovery can be made in geology equal in value to that which we owe to the genius of William Smith.--_Saturday Review_, No. 140.

DR. BUCKLAND’s GEOLOGICAL LABOURS.

Sir Henry De la Beche, in his Anniversary Address to the Geological Society in 1848, on presenting the Wollaston Medal to Dr. Buckland, felicitously observed:

It may not be generally known that, while yet a child, at your native town, Axminster in Devonshire, ammonites, obtained by your father from the lime quarries in the neighbourhood, were presented to your attention. As a scholar at Winchester, the chalk, with its flints, was brought under your observation, and there it was that your collections in natural history first began. Removed to Oxford, as a scholar of Corpus Christi College, the future teacher of geology in that University was fortunate in meeting with congenial tastes in our colleague Mr. W. J. Broderip, then a student at Oriel College. It was during your walks together to Shotover Hill, when his knowledge of conchology was so valuable to you, enabling you to distinguish the shells of the Oxford oolite, that you laid the foundation for those field-lectures, forming part of your course of geology at Oxford, which no one is likely to forget who has been so fortunate at any time as to have attended them. The fruits of your walks with Mr. Broderip formed the nucleus of that great collection, more especially remarkable for the organic remains it contains, which, after the labours of forty years, you have presented to the Geological Museum at Oxford, in grave recollection of the aid which the endowments of that University, and the leisure of its vacations, had afforded you for extensive travelling during a residence at Oxford of nearly forty-five years.

DISCOVERIES OF M. AGASSIZ.[34]

This great paleontologist, in the course of his ichthyological researches, was led to perceive that the arrangement by Cuvier according to organs did not fulfil its purpose with regard to fossil fishes, because in the lapse of ages the characteristics of their structures were destroyed. He therefore adopted the only other remaining plan, and studied the tissues, which, being less complex than the organs, are oftener found intact. The result was the very remarkable discovery, that the tegumentary membrane of fishes is so intimately connected with their organisation, that if the whole of the fish has perished except this membrane, it is practicable, by noting its characteristics, to reconstruct the animal in its most essential parts. Of the value of this principle of harmony, some idea may be formed from the circumstance, that on it Agassiz has based the whole of that celebrated classification of which he is the sole author, and by which fossil ichthyology has for the first time assumed a precise and definite shape. How essential its study is to the geologist appears from the remark of Sir Roderick Murchison, that “fossil fishes have every where proved the most exact chronometer of the age of rocks.”

SUCCESSION OF LIFE IN TIME.

In the Museum of Economic Geology, in Jermyn Street, may be seen ores, metals, rocks, and whole suites of fossils stratigraphically arranged in such a manner that, with an observant eye for form, all may easily understand the more obvious scientific meanings of the Succession of Life in Time, and its bearing on geological economies. It is perhaps scarcely an exaggeration to say, that the greater number of so-called educated persons are still ignorant of the meaning of this great doctrine. They would be ashamed not to know that there are many suns and material worlds besides our own; but the science, equally grand and comprehensible, that aims at the discovery of the laws that regulated the creation, extension, decadence, and utter extinction of many successive species, genera, and whole orders of life, is ignored, or, if intruded on the attention, is looked on as an uncertain and dangerous dream,--and this in a country which was almost the nursery of geology, and which for half a century has boasted the first Geological Society in the world.--_Saturday Review_, No. 140.

PRIMITIVE DIVERSITY AND NUMBERS OF ANIMALS IN GEOLOGICAL TIMES.