﻿304 Review of the New York Geological Reports. 



The preceding five figures of Pentamerus are all referred by Hall 

 to one species. The difference of form and size he attributes to 

 age and condition of the fossil. The species is supposed to be 

 identical with the P. oblongus of the calcareous beds of the Car- 

 adoc formation of England ; and the Clinton group is hence re- 

 garded as the American equivalent of that portion of Murchison's 

 Silurian system. A species closely allied to it occurs also in the 

 West, and the New York geologists seem to have concluded, that 

 the strata containing it must necessarily occupy the very same 

 geological position as the Pentamerus limestone of New York. 

 Mr. Conrad, speaking of the Pentamerus beds in Wisconsin, 

 affirms that when the Pentamerus in question is associated with 

 chain corals, as in that territory, the strata containing them are 

 never higher than the Clinton group of New York. But this is 

 by no means a settled point ; indeed, there are strong proofs that 

 the Pentamerus rock of Iowa and Wisconsin is a higher member 

 of the Protozoic system, than the Clinton group of New York. 

 The Pentamerus and Catenipora in the northwest are associated 

 with a variety of corals, most of them bearing a strong resem- 

 blance, and many of them evidently specifically identical with 

 Polyparia of the Wenlock and Dudley limestones of England, 

 which belong to the upper Silurian system ; whereas the Clin- 

 ton group has been placed by its describers in the lower Silurian 

 system. 



In Indiana the Pentamerus layers, though beneath, are in 

 close proximity to coralline beds containing many of the same 

 species of Polyparia, associated with the same Pentamerus as 

 in the territories. 



Besides the remains of the Pentamerus in question, in the West- 

 ern states and territories are almost invariably internal casts, 

 which give but an imperfect knowledge of the shell itself Close 

 comparison of complete fossil shells might perhaps prove the 

 western species to be distinct from the P. oblongus. 



Again, the evidence derived from the occurrence of the Cater 

 nipora escharoides is at best unsatisfactory, since it has so wide 

 a range. In New York this chain coral extends from the Clinton 

 group up to the Manlius water-limestone ; in the West it appears 

 to h^ve been found by Dr. Clapp even as high as the coal forma- 

 tion ; in England it ranges from the Llandeilo flags of the lower 

 Silurian through all the intervening beds up to the Aymestry 



