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Excerpt from The Paleontology of the Niagaran Limestone in the Chicago Area, Vol. 1: The Crinoidea The age of the strata which contain the Chicago fauna is late Niagaran, but little older than the Guelph formation of Canada. The formation in which the fossils are preserved is a dolomite, and the manner of preservation of the fossils is by no means so satisfactory as would be desirable. For the most part they are internal casts and external impressions; in only rare instances are the fossils themselves found preserved with any degree of perfection. For this reason it is not always practicable to make proper comparisons between Chicago spe cies and the same or allied species preserved in other localities under different conditions. In certain cases very excellent reproductions of the external Characters of some species have been secured by making wax casts from the natural moulds in the rock, and by the use of these casts, and such specimens as have been secured preserving the substance of the fossils, the characters, in many instances, have been made out with some degree of completeness. Some species, however, have not as yet afforded good specimens either of external moulds or of the substance of the fossil itself. 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.

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