104 llie Position of the Cincinnati Group. 



cephalopoda and Crustacea of the ocean, but never containing even a 

 fragment of a land invertebrate. 



This great thickness of the Lower Silurian rocks of North America 

 is fully equaled by the Lower Silurian of Europe, and especially of 

 England and Scotland, where it is estimated at 50,000 feet (Murchi- 

 son's Siluria, p. 174). And the development of animal life, as shown 

 by the fossil contents of the strata of Europe, was precisely the equiv- 

 alent of that in America. 



Overlying the Cincinnati Group, we have the Upper Silurian rocks, 

 which are subdivided in ascending order, into : 1st, Oneida conglomer- 

 ate ; 2d, Medina sandstone ; 3d, Clinton Group ; 4th, Niagara Group ; 

 5th, Onandaga Salt Group; and 6th, Lower Helderberg. 



The Oneida conglomerate is 400 feet thick in Pennsylvania, and 

 500 feet in New York. (Rep. 1st Dist., N. Y., p. 356.) 



The Medina sandstone is 350 feet thick in l!j"ew York, between the 

 mouth of the Niagara and Lewiston ; 618 feet at Barton, Canada, and 

 1,150 feet in Pennsylvania. (Geo. of Penn., vol. i., p. 105.) 



Lnmediately overlying the Cincinnati Group, in Ohio, and other 

 Avestern localities, we find either the Clinton or Niagara Group, and a 

 somewhat general change of species in animal life ; a few, however, pass 

 ,from the Cincinnati Group even to the Niagara. In New York and 

 other eastern localities, however, where the Oneida conglomerate and 

 Medina sandstone are interposed between the Cincinnati and Clinton 

 Groups, the fossils graduate from one group into the next higher, 

 v.-ithout greater changes than are to be found within each separate group, 

 and in such manner as to show that there was no break in animal 

 life. The same state of facts exist in England, Scotland, Wales, and 

 Bohemia, where the fossils pass from the Lower Silurian to the Upper 

 Silurian, in such manner as to demonstrate that there was no great dis- 

 turbance of the animals that lived in the sea, if indeed there is any 

 evidence to show that a greater change took place, either on land or 

 sea, than that which is taking place to-day, or takes place during the 

 deposition of any group of strata. 



Prof. Billings says that on the Island of Anticosti there is " a de- 

 posit of argilaceous limestone, 2,300 feet in thickness, regularly strati- 

 lied, in nearly horizontal and perfectly comformable beds. All the 

 facts tend to show that these strata were accumulated in a quiet sea, 

 in uninterrupted succession, during that period in which the upper 

 part of the Hudson River Group, the Oneida conglomerate, the Me- 

 dina sandstone, and the Clinton Group, were in the course of being 

 deposited in that part of the Paleozoic ocean now constituting the 

 State of New York and some of the countries adjacent. If this view 



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