Imágenes de página
PDF
ePub

the neighboring gulf was already characterized by its peculiar fauna. . . .

"The northern drift of the most southern latitudes is usually of the highest antiquity. In Scotland it rests on the older rocks, and is covered by stratified sand and clay, usually devoid of fossils, but in which at certain points . . . marine shells have been discovered. . . . Although a proportion of between 85 or 90 in 100 of the imbedded shells are of recent species, the remainder are unknown; and even many which are recent, now inhabit more northern seas, where we may, perhaps, hereafter find living representatives of some of the unknown fossils.

"The testaceous fauna of the boulder period in Scotland, England, and Ireland, has been shown by Prof. E. Forbes to contain a.much smaller number of species than that now belonging to the British seas. . . . Yet the species are nearly all of them now living either in the British or more northern seas, the shells of more arctic latitudes being the most abundant, and the most wide-spread throughout the entire area of the drift from North to South."—Lyell's Manual of Geol. pp. 124—126.

"M. Deshayes and Mr. Lyell have recently proposed a fourfold division of the marine formations of the tertiary series, founded on the proportions which their fossil shells bear to marine shells of Existing Species. To these divisions Mr. Lyell has applied the terms eocene, miocene, older-pliocene, and newer-pliocene, and has most ably illustrated their history in his Principles of Geology.

"The term eocene implies the commencement or dawn of the existing state of the animal creation; the strata of this series containing a very small proportion of shells referable to living species. The calcaire grossier of Paris and the London clay are familiar examples of this older tertiary, or eocene formation.

"The term miocene implies that a minority of the fossil shells, in formations of this period, are of recent species. To this are referred the fossil shells of Bordeaux, Turin, and Vienna.

"In formations of the older and newer-pliocene taken together, the majority of the shells belong to living species; the recent species in the newer being much more abundant than in the older division.

"To the older pliocene belong the Sub-Appenine marine formations and the English Clay; and to the newer-pliocene the more recent marine deposits of Sicily, Ischia, and Tuscany."—Dr. Bucldand's Bridgewater Treatise, pp. 78, 79.

A considerable number, also, of the fossil fish and land quadrupeds are of species that still exist. The tertiary strata which comprise all that are between the chalk formation and the diluvium, are of great depth, and are the depositories of by far the most important classes, especially of land animals.

"It appears that the animal kingdom was early established on the same general principles that now prevail; not only did the four present classes of vertebrata exist; and among mammalia, the orders pachydermata, carnivora, rodentia, and marsupialia, but many of the genera into which living families are distributed, were associated together in the same system of adaptations and relations which they hold to each other in the actual creation.

"The bones of all these animals found in the earliest series of the tertiary deposits are accompanied by the remains of reptiles, such as now inhabit the fresh waters of warm countries, e. g. the crocodile, emys, and tryonix.

"The second or miocene system of tertiary deposits contains an admixture of the extinct genera of lacustrine mammalia of the first or eocene series, with the earliest forms of genera which exist at the present time.

"The third and fourth of pliocene divisions of the tertiary fresh-water deposits,. . . abound in extinct species of pachydermata, e. g. elephant, rhinoceros, hippopotamus, and horse, together with the extinct genera mastodon. With them also occur the first abundant traces of the ruminantia, e. g. oxen and deer.

"The seas, also, of the miocene and pliocene periods were inhabited by marine mammalia, consisting of whales, dolphins, seals, walrus, and the lamantin, or manati, whose existing species are chiefly found near the coasts and mouths of rivers in the torrid zone.—Buckland's Bridg. Treatise, pp. 87-92.

"The largest, the most ferocious, and the least useful of the pliocene species have perished; but the horse, the ass, the hog, probably the smaller wild ox, the goat, the reddeer, and roe, and many of the diminutive quadrupeds remain It is probable that the horse and ass are descendants of a species of pliocene antiquity in Europe. There is no anatomical character by which the present wild boar can be distinguished specifically from that which was contemporary with the mammoth. All the species of European pliocene Bovidae come down to the historical period, and the aurochs and musk ox still exist. . . . There is evidence that the great bos primigenius, and the small bos longifrons, which date by fossils from the time of the mammoth, continued to exist in this island after it became inhabited by man. The small short-horned pliocene ox is most probably still preserved in the mountain varieties of our domestic cattle. The great urus seems never to have been tamed, but to have been finally extirpated in Scotland. Of the cervine tribe, the red-deer and the roebuck still exist in the mountainous districts of the north."—R. Owen's Hist. Brit. Fossil Mammalia and Birds, Introd. p. xxxii.

The period supposed by geologists to have intervened between the deposition of the eocene strata, in which a share of these fossils is found, and the epoch of the six days' creation, they regard as immense. Thus Prof. Owen says:

"With the last layer of the eocene deposits, we lose in this island every trace of the mammalia of that remote period. The imagination strives in vain to form an idea commensurate with the evidence of the intervening operations which continental geology teaches to have gradually and successively taken place—of the length of time that elapsed be/ore the foundations of England were again sufficiently settled to serve as the theatre of life to another race of warmblooded quadrupeds.

"In the endeavor to trace the origin of our existing mammalia, I have been led to view them as descendants of a portion of a peculiar and extensive mammalian Fauna, which overspread Europe and Asia at a period geologically recent, yet incalculably remote, and long anterior to any evidence or record of the human race."Hist. Brit. Fos. pp. xxi-xxxv.

Sir C. Lyell refers the strata in which they are imbedded to an equally remote age.

"It would be rash to infer that these quadrupeds "—the mastodons, found in New Jersey and New York—" were mired in modern times, unless we use that term strictly in a geological sense. I have shown that there is a fluviatile deposit in the valley of the Niagara, containing shells of the genera Melania, Lymnea, Planorbis, Valvata, Cyclas, Unio, and Helix, &c, all of recent species, from which the bones of the great mastodon have been taken in a very perfect state. Yet the whole excavation of the ravine, for many miles below the Falls, has been slowly effected, since that fluviatile deposit was thrown down.

"Whether or not, in assigning a period of more than 30,000 years for the recession of the Falls from Queenstown to their present site, I have over or under estimated the time required for that operation, no one can doubt that a vast number of centuries must have elapsed before so great a

« AnteriorContinuar »