102 The American Geologist. Feb.i89t 
existence is not necessarily inferred. In neighboring parts of In- 
diana similar conditions prevailed in axial regions of the anti- 
clinal. 
The exposed portions of the Cincinnati group formations in 
Ohio during later than Clinton times being thus limited to that 
part of the anticlinal immediately adjoining the Ohio river, or 
even perhaps being confined to regions south of this limit, the 
area covered by the Clinton being still an area of deposition, how 
could the anticlinal area supply the immense mass of strata of 
later than Clinton age which cover and surround the anticlinal in 
Ohio. I doubt if mathematical calculations would not show that 
the erosion which has taken place over the entire area of Cincin- 
nati rocks now exposed, would be insufficient to provide the ma- 
terials for Upper Silurian, Devonian and Waverly formations in 
Ohio and Indiana alone, not considering the great mass of these 
formations in Kentucky and Tennessee. The continuous mantle of 
Clinton rocks in Ohio makes a source from more southern anti- 
clinal exposures perfectly inadequate, while the different chemical 
constitution of succeeding formations makes their source from re- 
erosion of Clinton strata also improbable — not considering for the 
present the improbability of much erosion in the Clinton before 
the deposition of the Niagara shales, which are found almost 
above every exposure of Clinton rocks in southern Ohio. These 
shales, however, already proclaim a widely different chemical con- 
stitution from that offered by Clinton rocks in these southern re- 
gions of Ohio. 
If the anticlinal was in existence in Lower Silurian times, and 
provided the materials for later formations, the character of de- 
posits on the eastern and on the western sides of this axis should 
not be essentially different, at least in the immediate vicinity of 
the anticlinal. What are the facts? Medina and Clinton forma- 
tions in Tennessee are confined to the eastern side of the axis, and 
apparantly gradually become more attenuated in approaching the 
same, disappearing before reaching it. Niagara formations in 
this state, on the contrary, have a greater development west of 
the anticlinal, become attenuated eastward on approaching the 
crest of the anticlinal, beyond which they do not extend far, if 
at all. The Lower Helderberg occurs only west of the anticlinal, 
and also becomes attenuated eastward, disappearing long before 
