154: NEW YORK STATE MUSEUM 



The cataract of Niagara is produced by the passage of the river 

 over this limestone and shale; and from being a well known and 

 extremely interesting locality, as well as exhibiting the greatest 

 natural development of these rocks within the limits of the state, 

 this name has been adopted for its designation. 



Standing on the upper suspension bridge at Niagara Falls, one 

 sees in the precipice, above the Clinton limestone, a sloping bank 

 of soft gray shale about 80 feet thick, above which succeeds a 

 thick series of layers of limestone forming the brink of the 

 rocky wall: these are the Niagara shale and the Niagara lime- 

 stone. The great cataract pours over their edges; and its ver- 

 tical descent is owing to the fact that the soft shale below wears 

 away more rapidly than the hard limestone which forms the top 

 of the fall, thus maintaining a recess behind the descending sheet 

 of water. These rocks are perfectly exhibited in the gorge of 

 the Niagara river, especially along the Niagara Falls and Lewis- 

 ton railroad. 



The limestone at Niagara is about 160 feet thick (of which only 

 the lower part is seen at the falls); at Rochester it is about 70 

 feet thick. The shale decomposes rapidly where exposed to the 

 air, until it resembles a deposit of gray clay. It contains thin 

 layers of limestone in many places, the surfaces of which are 

 often covered with beautiful small corals of several species, and 

 the shale itself contains them in great numbers. The ( deep cut ' 

 of the canal above Lockport is through the Niagara limestone, 

 some layers of which there form a massive and beautiful build- 

 ing stone. The same limestone and shale form the upper falls 

 of the Genesee at Rochester. 



Salina Groilp, or Onondaga Salt Group 

 The next series of strata in upward succession is a group of 

 shales and thin limestones, the whole of which in central and 

 western New York attains a thickness of nearly 1,000 feet. 

 Its lower part in central New York is composed for several 

 hundred feet of a soft red shale or hardened clay, especially 

 conspicuous along the Erie canal in Madison county. Its upper 



