Proceedings of the Biological Society of Washington Volume 1-3 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1882 Excerpt: ...related to faunas which are known to have existed in subsequent periods, as well as to certain fresh-water mollusks now living in North America. A few species belonging to the fresh-water family Unionidae have been discovered in Cretaceous strata of the western portion of this continent, but they all appear to be of different types from any of the family now living. I take this to be an indication that the fresh waters in which those Uniones lived were not continued to later periods, as some other ancient streams of fresh water were, together with their molluscan faunas, and that the lines of descent of those mollusks were consequently cut off and their types extinguished. While many rivers have persistently held their ground through several geological periods, despite even the elevation of mountain ranges across their course; the fact that great numbers of them have been destroyed in past geological time by the physical changes which have taken place in the regions they have occupied, is too evident to be questioned. One of the many examples of the destruction of bodies of fresh water which have become established upon the earth in former geological times is suggested by the presence of a true estuary deposit among the. Cretaceous strata of Northern Utah. This deposit, which is a rare one of the kind, was evidently formed at the western border of the oceanic belt, which, it is understood, then traversed the whole North American area in a northward and southward direction, between two separate continental areas, and at the mouth of a river which then drained part of the western area. The region which that oceanic belt then occupied is now the heart of the continent, and all traces of the ancient river referred to are obliterated. Furthermore, the district w...