File:Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct - for the use of schools and colleges (1870) (14782857155).jpg

Identifier: outlinesofcompar00agas (find matches)
Title: Outlines of comparative physiology touching the structure and development of the races of animals, living and extinct : for the use of schools and colleges
Year: 1870 (1870s)
Authors: Agassiz, Louis, 1807-1873 Gould, Augustus A. (Augustus Addison), 1805-1866 Wright, Thomas, 1809-1884
Subjects: Physiology, Comparative Zoology
Publisher: London : Bell & Daldy
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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nges.The Plutonic rocks, as well as the metamorphic rocks, are not always con-fined to the lower levels, but they are often seen rising to considerableheights, and forming mary of the loftiest peaks of the globe. The formeralso penetrate, in many cases, like veins, through the whole mass of thestratified and metamorphic layers, and expand at the surface ; as is the casewith the trap dykes, and as lava streams actually do now (fig. 376, T. L.) 392 GEOLOGICAL SUCCESSION OF ANIMALS. surface have been elevated to great heights, in the form ofmountains ; and hence it is that fossils are sometimes found atthe summit of the highest mountains, though the rocks con-taining them were originally formed at the bottom of the sea.But even when folded, or partly broken, their relative age maystill be determined by an examination of the ends of the up-turned strata, where they appear or crop out in succession, atthe surface, or on the slopes of mountains, as seen in the dia-gram (fig. 376). Fig. 376.
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§ 649. The sedimentary rocks are the only ones containinganimal and vegetable remains. These are found imbedded inthe rock, just as we should find them in the mud now depositedat the bottom of the sea, if laid dry. The strata containingfossils are numerous. The comparison and detailed study ofthem belongs to geology, of which Palaeontology forms anessential part. A group of strata extending over a certaingeographical extent, all of which contain some fossils in com-mon, no matter what may be the chemical character of therock, whether it be limestone, sand, or clay, is termed ageological Formation. Thus, the coal beds, with the inter-vening slates and grits, and the masses of limestone betweenwhich they often lie, constitute but one formation,—the car-boniferous formation. § 650. Among the stratified rocks, we distinguish ten prin-cipal formations, each of wrhich indicates an entirely newera in the earths history ; while each of the layers com-posing a formation indicates but some

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