96 



HISTORICAL PALAEONTOLOGY. 



stones, and limestones (the " Cincinnati'" rocks proper). The 

 exact paraUehsm of the Trenton and Cincinnati groups with 

 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 : — 



Generalised Section of the Lower Silurian Rocks 

 OF North America. 



Fig- 35- 



Medina Sandstone (base of 

 Upper Silurian). 



O* 



\. • , .^\~ ^ 



c o " e 



e Q e o 



Cincinnati Group proper. 



Utica Slates. 



Trenton Limestone. 



Black River Limestone. 



Bird's-eye Limestone. 



• Chazy Limestone. 



Quebec Shales (Levis Beds). 



Calciferous Sand-rock. 

 — --Potsdam Sandstone. 



