NIAGARA FALLS AND VICINITY 121 



equivalent of the Oriskany sandstone of eastern New York, though 

 no fossils have been found in them. AVith the exception of these 

 layers the Lower Devonic strata are wanting in this region. 



The Middle Devonic is however well represented in the Niagara 

 region by the Onondaga limestone. This rock, which, as has been 

 shown, rests in most cases directly on the Manlius limestone, con- 

 sists of a lower crystalline and highly fossiliferous portion, and an 

 upper mass full of layers of hornstone or chert which on weathered 

 surfaces stand out in relief. This part of the formation is generally 

 known as the Corniferous limestone, in reference to the layers of 

 chert which make the rock unfit for other use than rough building. 

 Owing to the presence of the hornstone, this rock effectually re- 

 sists the attacks of the atmosphere, and hence its line of out- 

 crop is generally marked by a prominent topographic relief feature, 

 the second escarpment of western New York i. e. the inface of the 

 Onondaga cuesta. 



The chert-free lower member of this formation varies greatly in 

 thickness even within a limited territory. It is in places extremely 

 rich in corals, and outcrops of this rock show all the characteristics 

 of an ancient coral reef. 



History of the Niagara region during Siluric time 



We have now gathered data for a brief synopsis of the history of 

 this region during Siluric time. Much still remains to be learned, 

 but from what is known we can trace at least in outline the sequence 

 of geologic events which characterized that ancient era of the earth's 

 history in this vicinity. 



When the Siluric era opened, New York, with portions of Penn-- 

 sylvania and southern Ontario, was covered by the shallow Medina 

 sea. This sea appears to have been of the nature of a mediter- 

 ranean body of water, which later changed to a bay opening toward 

 the southwest. This ''Bay of New York", as we shall call it, came 

 into existence by the orogenic disturbances which marked the transi- 

 tion from the Ordovicic to the Siluric era, and as a result of which 

 the Taconic mountain range, with the Green mountains and the 

 corresponding Canadian ranges, were elevated. This cut off the 



