BRYOZOAN FAUNA OF THE ROCHESTER SHALE. 5 
CORRELATION. 
For various reasons the exact correlation of the several members of the New York 
Niagaran with strata of the same age elsewhere has not met with complete satisfaction. 
The lithologic and faunal differences in beds which should apparently be correlated strati- 
graphically are so great that it seems evident for these reasons alone that the rocks must 
have been deposited in separate basins. For lack of sufficient collections the evidence 
afforded by the bryozoa in the correlation of the various Niagaran deposits is not yet com- 
plete, but the present study of the Rochester shale fauna and of collections from the Osgood 
beds of Indiana indicates the undoubted equivalence of at least these two formations. 
The Niagaran strata exposed along the western flank of the Cincinnati anticline in southern 
Indiana, Kentucky, Tennessee, and northern Alabama have been divided into the following 
formations :« 
5. Louisville limestone. 
4 Waldron shale. 
3. Laurel limestone. 
2. Osgood shale and limestone. 
1. Clinton limestone. 
The distribution and paleontological characteristics of these rocks have been discussed by 
Foerste in various articles, and the following description of the Osgood formation is based 
mainly on his work: 
Several thin limestone layers having a total thickness of 8 to 15 inches form the base of 
the Osgood formation. Following these are 11 to 16 feet of clay, which in Kentucky is 
usually soft, but in Indiana is somewhat indurated. In other sections this lower Osgood 
clay is overlain by a crinoidal limestone often 5 feet in thickness, and this in turn by the 
upper Osgood clay variable in thickness but sometimes reaching 5 feet. 
According to Foerste, Pisocrinus, Stephanocrinus, Holocystites, Rhyjxchotreta, Spirifer, 
Cyrtia, and Nucleospira make their first appearance in the Osgood formation. Associated 
with these, especially in the clayey partings of the limestones, are the bryozoa identified in 
this paper. Most all of the nonbryozoan genera and in fact identical species even may 
occur in the Rochester shale. The evidence presented by the bryozoa themselves is shown 
in the table below. 
In regard to the correlation of the Osgood fauna, Foerste & remarks as follows: " In many 
respects the Osgood fauna is a forerunner of that found in the Waldron. It corresponds to 
the reef fauna at the top of the Clinton of New York, where it occurs in the limestones 
exposed in the lens-like cross sections just beneath the Rochester shale." 
While the writer agrees that the Osgood fauna is a forerunner of the Waldron, and that it 
also may correspond in part to the reef fauna, comparisons of the bryozoan elements of the 
faunas seem to show beyond question that the Osgood is chiefly if not exactly comparable 
with the Rochester shale. 
c Foerste, A. F., Twenty-eighth Ann. Rept. Indiana Dept. Geoi. Nat. Res., 1904. 
b Op. cit., p. 30. 
