38 
PALAEONTOLOGY 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 beds 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 
Lockport, or the banks of the Genesee river below Rochester; so that were 
