96 HISTORICAL PALEONTOLOGY. 
stones, and limestones (the “‘ Cincinnati” rocks proper). The 
exact parallelism 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). 
5 
O 
Z 
- Cincinnati Group proper. 
> 
= 
Z, 
is 
oO 
2 =------ Utica Slates. 
a 
5 
4 A Sete = ~Trenton Limestone. 
>) 
S 
s LL 
a) 0) 0 Se eee ee ee eee ee -Black River Limestone. 
4 
arencrge VO) Pe ie Wa On ee Bird’s-eye Limestone. 
a (Tt].----.-Chazy Limestone. 
Y => 
5 
5 
a =... (Quebec Shales (Levis Beds). 
es 
= 
& 
= 
oem CE et a ee aay eee ..Calciferous Sand-rock. 
ee BS Potsdam Sandstone. 
