THE LOWER SILURIAN PERIOD. 



97 



the subdivisions of the Welsh Silurian series can hardly be 

 stated positively. Probably no precise equivalency exists ; 

 but there can be no doubt but that the Trenton and Cincin- 

 nati groups correspond, as a whole, with the Llandeilo and 

 Caradoc groups of Britain. The subjoined diagrammatic 

 section (fig. 35) gives a general idea of the succession of the 

 Lower Silurian rocks of North America : 



GENERALIZED SECTION OF THE LOWER SILURIAN ROCKS 

 OF NORTH AMERICA. 



Fig. 35- 



_ | Medina Sandstone (base of 

 Upper Silurian). 



Cincinnati Group proper. 



Utica Slates. 

 Trenton Limestone. 



Black River Limestone. 

 Bird's-eye Limestone. 

 Chazy Limestone. 



Quebec Shales (Levis Beds). 

 Calciferous Sand-rock. 



o I 



Potsdam Sandstone. 



