Excerpt from Geological Survey of Illinois, Vol. 2: Palaeontology But the materials of which even our hardest stratified rocks are composed were not, in every instance, entirely and directly derived from the wreck of pre-existing solid rocks, for there was some working over of the same materials, without the action of the intervening process Of consolidation; and the remains of corals, crinoids, shells, and other marine organisms, often con tributed much the larger portion of the substances composing marine strata, while in other instances the remains of land and fresh-water animals and plants, carried in by streams, form con siderable portions of extensive estuary and lacustrine formations. Hence, as the animals and plants of each of the great epochs, although mainly different from those of the preceding and fol lowing ages, presented, with occasional exceptions, a remarkable general similarity during each individual period, over the entire globe, their fossil remains furnish the Geologist an unerring guide in the identification of strata, and the determination of their position in the series, as well as of their relative ages. As the learned Antiquary determines the age and history of some ruined city, in regard to which both written and traditional history are silent, by a careful study of the inscriptions upon its walls, or of the seals, coins, medals, etc, found amongst its rub bish, so does the skillful Palaeontologist determine the period of the earth's history to which an outcrop or stratum of rock belongs, and its place 'in the geological series, by inspecting its imbedded organic remains. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.