•8 . PALJiONTOLOGY OF NEW-YORK. 



into Illinois, where it still retains the characters and the fossils which 

 mark its occurrence in Wisconsin. 



Throughout much of this extent, the limestone is not in a condition to 

 preserve the smaller and more delicate fossils, and the larger corals are 

 often the only conspicuous forms. The Pentamerus oblongus, which, within 

 New- York, is confined to the calcareous heds of the Clinton group, is every- 

 where, in the west, a characteristic fossil of the Niagara limestone ; and in 

 Wisconsin and Illinois, it acquires a development in size and in numbers 

 of individuals truly surprising. In many western localities the most con- 

 spicuous and prevailing fossils of the Niagara limestone are large cepha- 

 lopods of the Genera Orthoceras, Gomphoceras, Lituites, etc. 



In the neighborhood of Milwaukie and of Waukesha, the peculiarities 

 in the development of the different members of this limestone group have 

 induced Mr. I. A. Lapham to constitute a distinct member, the Waukesha 

 limestone. From an examination of the localities, and a comparison of the 

 fossils, I have not found sufficient evidence to warrant a separation from 

 the Niagara group, and must regard the peculiar features as a phase of 

 some portions of the Niagara limestone, and a condition not likely to be 

 persistent. 



The limestone of Waukesha consists of thin-bedded, fine-grained layers, 

 which in the original condition must have been an impalpable calcareous 

 mud, supporting during its deposition scarcely anything except a few 

 orthoceratites and some other cephalopodous shells. In other localities the 

 irregular heavier bedded porous limestone, with corals and other fossils, 

 bears a more complete correspondence with the Niagara limestone as we 

 know it in its eastern localities. 



These varieties of the formation, being the result of varying conditions 

 , in the ocean of the Niagara period, have furnished some new forms of 

 animal life ; but the extent here traced from the western limits of New- 

 York, around a great curve measuring twelve degrees of longitude, has 

 produced altogether fewer species of fossils than the single locality of 

 Lock port, or the banks of the Genesee river below Rochester ; so that were 



