106 



rjLtJkosrohoai of nbw-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 tliickness 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 pateozoic 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 fossilifsrous. Farther eastward there ar« several points where the group may 



