Part 1 (2/2)
III. The successive deposition of the sedimentary rocks.
As a corollary to these, the hypothesis of the upheaval of the earth's crust follows--upheavals having produced local revolutions. The result of these upheavals has been to superimpose new materials upon the older rocks, introducing extraneous rocks called _Eruptive_, beneath, upon, and amongst preceding deposits, in such a manner as to change their nature in divers ways. Whence is derived a third cla.s.s of rocks called _Metamorphic_ or altered _rocks_, our knowledge of which is of comparatively recent date.
FOSSILS.
The name of _Fossil_ (from _fossilis_, dug up) is given to all organised bodies, animal or vegetable, buried naturally in the terrestrial strata, and more or less petrified, that is, converted into stone. Fossils of the older formations are remains of organisms which, so far as species is concerned, are quite extinct; and only those of recent formations belong to genera living in our days. These fossil remains have neither the beauty nor the elegance of most living species, being mutilated, discoloured, and often almost shapeless; they are, therefore, interesting only in the eyes of the observer who would interrogate them, and who seeks to reconstruct, with their a.s.sistance, the Fauna and Flora of past ages. Nevertheless, the light they throw upon the past history of the earth is of the most satisfactory description, and the science of fossils, or palaeontology, is now an important branch of geological inquiry. Fossil sh.e.l.ls, in the more recent deposits, are found scarcely altered; in some cases only an impression of the external form is left--sometimes an entire cast of the sh.e.l.l, exterior and interior. In other cases the sh.e.l.l has left a perfect impression of its form in the surrounding mud, and has then been dissolved and washed away, leaving only its mould. This mould, again, has sometimes been filled up by calcareous spar, silica, or pyrites, and an exact cast of the original sh.e.l.l has thus been obtained. Petrified wood is also of very common occurrence.
These remains of an earlier creation had long been known to the curious, and cla.s.sed as _freaks of Nature_, for so we find them described in the works of the ancient philosophers who wrote on natural history, and in the few treatises on the subject which the Middle Ages have bequeathed to us. Fossil bones, especially those of elephants, were known to the ancients, giving rise to all sorts of legends and fabulous histories: the tradition which attributed to Achilles, to Ajax, and to other heroes of the Trojan war, a height of twenty feet, is attributable, no doubt, to the discovery of the bones of elephants near their tombs. In the time of Pericles we are a.s.sured that in the tomb of Ajax a _patella_, or knee-bone of that hero, was found, which was as large as a dinner-plate.
This was probably only the patella of a fossil elephant.
The uses to which fossils are applied by the geologist are--First, to ascertain the relative age of the formations in which they occur; secondly, the conditions under which these were deposited. The age of the formation is determined by a comparison of the fossils it contains with others of ascertained date; the conditions under which the rocks were deposited, whether marine, lacustrine, or terrestrial, are readily inferred from the nature of the fossils. The great artist, Leonardo da Vinci, was the first to comprehend the real meaning of fossils, and Bernard Palissy had the glory of being the first modern writer to proclaim the true character of the fossilised remains which are met with, in such numbers, in certain formations, both in France and Italy, particularly in those of Touraine, where they had come more especially under his notice. In his work on ”Waters and Fountains,” published in 1580, he maintains that the _figured stones_, as fossils were then called, were the remains of organised beings preserved at the bottom of the sea. But the existence of marine sh.e.l.ls upon the summits of mountains had already arrested the attention of ancient authors. Witness Ovid, who in Book XV. of the ”Metamorphoses” tells us he had seen land formed at the expense of the sea, and marine sh.e.l.ls lying dead far from the ocean; and more than that, an ancient anchor had been found on the very summit of a mountain.
”Vidi factas ex aequore terras, Et procul a pelago conchae jacuere marinae, Et vetus inventa est in montibus anchora summis.”
Ov., _Met._, Book xv.
The Danish geologist Steno, who published his princ.i.p.al works in Italy about the middle of the seventeenth century, had deeply studied the fossil sh.e.l.ls discovered in that country. The Italian painter Scilla produced in 1670 a Latin treatise on the fossils of Calabria, in which he established the organic nature of fossil sh.e.l.ls.
The eighteenth century gave birth to two very opposite theories as to the origin of our globe--namely, the _Plutonian_ or igneous, and the _Neptunian_ or aqueous theory. The Italian geologists gave a marked impulse to the study of fossils, and the name of Vallisneri[1] may be cited as the author to whom science is indebted for the earliest account of the marine deposits of Italy, and of the most characteristic organic remains which they contain. Lazzaro Moro[2] continued the studies of Vallisneri, and the monk Gemerelli reduced to a complete system the ideas of these two geologists, endeavouring to explain all the phenomena as Vallisneri had wished, ”without violence, without fiction, without miracles.” Ma.r.s.elli and Donati both studied in a very scientific manner the fossil sh.e.l.ls of Italy, and in particular those of the Adriatic, recognising the fact that they affected in their beds a regular and constant order of superposition.[3]
[1] Dei corpi marini, &c., 1721.
[2] Sui crostaccei ed altri corpi marini che se trovano sui monti, 1740.
[3] Consult Lyell's ”Principles of Geology” and the sixth edition of the ”Elements,” with much new matter, for further information relative to the study of fossils during the last two centuries.
In France the celebrated Buffon gave, by his eloquent writings, great popularity to the notions of the Italian naturalists concerning the origin of fossil remains. In his admirable ”epoques de la Nature” he sought to prove that the sh.e.l.ls found in great quant.i.ties buried in the soil, and even on the tops of mountains, belonged, in reality, to species not living in our days. But this idea was too novel not to find objectors: it counted among its adversaries the bold philosopher who might have been expected to adopt it with most ardour. Voltaire attacked, with his jesting and biting criticism, the doctrines of the ill.u.s.trious innovator. Buffon insisted, reasonably enough, that the presence of sh.e.l.ls on the summit of the Alps was a proof that the sea had at one time occupied that position. But Voltaire a.s.serted that the sh.e.l.ls found on the Alps and Apennines had been thrown there by pilgrims returning from Rome. Buffon might have replied to his opponent, by pointing out whole mountains formed by the acc.u.mulation of these sh.e.l.ls.
He might have sent him to the Pyrenees, where sh.e.l.ls of marine origin cover immense areas to a height of 6,600 feet above the present sea-level. But his genius was averse to controversy; and the philosopher of Ferney himself put an end to a discussion in which, perhaps, he would not have had the best of the argument. ”I have no wish,” he wrote, ”to embroil myself with Monsieur Buffon about sh.e.l.ls.”
It was reserved for the genius of George Cuvier to draw from the study of fossils the most wonderful results: it is the study of these remains, in short, which, in conjunction with mineralogy, const.i.tutes in these days positive geology. ”It is to fossils,” says the great Cuvier, ”that we owe the discovery of the true theory of the earth; without them we should not have dreamed, perhaps, that the globe was formed at successive epochs, and by a series of different operations. They alone, in short, tell us with certainty that the globe has not always had the same envelope; we cannot resist the conviction that they must have lived on the surface of the earth before being buried in its depths. It is only by a.n.a.logy that we have extended to the primary formations the direct conclusions which fossils furnish us with in respect to the secondary formations; and if we had only unfossiliferous rocks to examine, no one could maintain that the earth was not formed all at once.”[4]
[4] ”Oss.e.m.e.nts Fossiles” (4to), vol. i., p. 29.
The method adopted by Cuvier for the reconstruction and restoration of the fossil animals found in the plaster-quarries of Montmartre, at the gates of Paris, has served as a model for all succeeding naturalists; let us listen, then, to his exposition of the vast problem whose solution he proposed to himself. ”In my work on fossil bones,” he says, ”I propose to ascertain to what animals the osseous fragments belong; it is seeking to traverse a road on which we have as yet only ventured a few steps. An antiquary of a new kind, it seemed to me necessary to learn both to restore these monuments of past revolutions, and to decipher their meaning. I had to gather and bring together in their primitive order the fragments of which they are composed; to reconstruct the ancient beings to which these fragments belonged; to reproduce them in their proportions and with their characteristics; to compare them, finally, with others now living on the surface of the globe: an art at present little known, and which supposes a science scarcely touched upon as yet, namely, that of the laws which preside over the co-existence of the forms of the several parts in organised beings. I must, then, prepare myself for these researches by others, still more extended, upon existing animals. A general review of actual creation could alone give a character of demonstration to my account of these ancient inhabitants of the world; but it ought, at the same time, to give me a great collection of laws, and of relations not less demonstrable, thus forming a body of new laws to which the whole animal kingdom could not fail to find itself subject.”[5]
[5] ”Oss.e.m.e.nts Fossiles” (4to), vol. i., pp. 1, 2.
”When the sight of a few bones inspired me, more than twenty years ago, with the idea of applying the general laws of comparative anatomy to the reconstruction and determination of fossil species; when I began to perceive that these species were not quite perfectly represented by those of our days, which resembled them the most--I no longer doubted that I trod upon a soil filled with spoils more extraordinary than any I had yet seen, and that I was destined to bring to light entire races unknown to the present world, and which had been buried for incalculable ages at great depths in the earth.
”I had not yet given any attention to the published notices of these bones, by naturalists who made no pretension to the recognition of their species. To M. Vaurin, however, I owe the first intimation of the existence of these bones, with which the gypsum-quarries swarm. Some specimens which he brought me one day struck me with astonishment; I learned, with all the interest the discovery could inspire me with, that this industrious and zealous collector had already furnished some of them to other collectors. Received by these amateurs with politeness, I found in their collections much to confirm my hopes and heighten my curiosity. From that time I searched in all the quarries with great care for other bones, offering such rewards to the workmen as might awaken their attention. I soon got together more than had ever been previously collected, and after a few years I had nothing to desire in the shape of materials. But it was otherwise with their arrangement, and with the reconstruction of the skeleton, which could alone lead to any just idea of the species.
”From the first moment of discovery I perceived that, in these remains, the species were numerous. Soon afterwards I saw that they belonged to many genera, and that the species of the different genera were nearly the same size, so that size was likely rather to hinder than aid me.
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