106 
PALEONTOLOGY OF NEW-YORK. 
NIAGARA GROUP, 
The rocks of this group, where best developed in western New-York, consist of a mass 
of shale succeeded by one of limestone, the passage from the former to the latter taking place 
by the gradual increase of calcareous matter. The upper or terminating limestone of the Clinton 
group is succeeded by a soft argillo-calcareous shale, which maintains its character unchanged 
for a thickness of eighty to one hundred feet. Throughout the greater part of this it abounds 
in fossils, nearly all of which are quite distinct from those in the beds of the Clinton group. 
The limestone is of equal or greater thickness than the shale ; its lower part thin-bedded 
and argillaceous, becoming gradually more calcareous. A thick bed near the lower part 
is almost entirely composed of crinoidal joints, and comminuted fragments of corals, shells 
and crinoids. This portion of the mass contains, in a more or less perfect state of preserva¬ 
tion, the remains of many species which are more entire in the shale below. In the central 
and higher portions of this limestone there are few fossils besides corals, and these are often 
partially dissolved and their places filled by crystalline matter. This limestone is remarkable 
for the numerous cavities lined with various forms of calcareous spar, and others filled with 
sulphate of strontian, anhydrite or selenite. Fluor spar, and sulphurets of zinc and iron, are 
occasionally found in the same connexion. These cavities vary in size from the smallest dimen¬ 
sions to the extent of two or three feet; and in a great number of instances, and probably 
in all, they were originally occupied by some fossil body, which has been partially or en¬ 
tirely removed by solution. In many instances the masses of selenite or anhydrite still retain 
portions of some coral, included within the mass ; while in others a small portion of the 
fossil is preserved in connection with the surrounding stone, and envelopes the crystalline 
mass in such a manner as to show that the whole space has once been occupied by the same. 
In many of the masses of coral, still preserved, there are cavities occupied by crystals of 
sulphate of strontian, and others divided by plates of selenite ; and many more where these 
crystals have been removed, leaving the cavities. It is evident, therefore, that in a rock where 
so many species of fossils have been partially or entirely obliterated, we can not present its 
entire palaeozoic characters ; and if we were able to trace this rock where its condition is such 
as to preserve all the imbedded remains, we should make large accessions to the species 
already known. 
This group of rocks is better developed, and the exposures more favorable, in the vicinity 
of Niagara Falls and Lockport, than in any other part of the State. At Rochester, also, the 
two masses are well developed, and the exposure of the shale very complete. Farther to the 
east, the group has much diminished ; and though the limestone and shale are both visible at 
Wolcott and other points in Wayne county, the former has much diminished in thickness, and 
the latter is less fossiliferous. Farther eastward there are several points where the group may 
