98 
PALEONTOLOGY OF NEW-YORK. 
I have therefore adopted the name of the locality where the beds are 
best developed, for designating the entire group. The fossils are in 
some degree restricted in their vertical range, where the physical 
characters of the strata present the distinctive varieties peculiar to the 
subdivisions. Where, however, lithological character is more uniform 
throughout, the fossils are less restricted; and it would be impossible to 
indicate limits to any of the species below the Upper Pentamerus beds. 
This terminal member of the group does not everywhere exist; but 
where occurring, it is marked by a species of Pentamerus having nearly 
the same form as P. galeatus, but always smooth, and possessing other 
characters by which it can readily be distinguished from that species. 
Associated with this Pentamerus are several species of Rhynchonella, 
equally restricted in their vertical range; as well as a single Spirifer, of 
which only one specimen has been found, in a lower bed. A few species 
at the base of the formation are likewise very much restricted in their 
vertical range, as far as the formation has been examined. 
The Oriskany sandstone rests directly upon the upper member of the 
Lower Helderberg group. This rock is usually highly fossiliferous, being 
often composed of a mass of shells closely packed together. It is some¬ 
times, however, quite non-fossiliferous, and consists of a thin band of 
dark-colored, compact, siliceous rock, which graduates into the arenaceous 
shaly mass above. 
Although usually very distinct from the limestones below, there are 
nevertheless localities where a passage occurs between the two rocks ; 
and in such instances, some of the fossils, usually restricted to the lower 
beds, pass into those above. Instances of this kind occur in Maryland ; 
and from the collections of the Canada Survey, by Sir William E. Logan, 
we are prepared to find in some parts of the continent an intimate 
blending of these formations. 
In this volume, the fossils of the Lower Helderberg group, and those 
of the Oriskany sandstone, are arranged as fossils from separate and 
successive groups, which is fully justified by their physical condition in 
the State of New-York. 
