Devonian Era in the Ohio Basin. — Claypole. 91 
Character of Sea. — Without too closely assuming an iden- 
tity with the strata of the eastern states, the lower parts of 
the Ohio shale must be the correlative of the beds overlying the 
Hamilton of New York, Pennsylvania, etc. We may safely 
then trace its outcrop from Canada along almost the same lines 
as those of its predecessor : thence through western and central 
Xew York, beyond which point it curves into Pennsylvania, 
traverses the central part of that state and then dives with the 
Harhilton beneath the Allegheny mountains. Reappearing in 
Ohio, it meets the line of the Cincinnati promontory, but the ev- 
idence fails to show to what extent it overlapped the earlier 
formations along its eastern slope. The depression in southern 
Ohio, where the outcrop of the Corniferous limestone and the 
Corniferous-Hamilton is concealed by the transgression of the 
shale, probably included the arch and allowed its deposition 
over the edges of some of the older, strata. But as both have 
heeii completely removed by erosion it is not possible to deter- 
mine the extent of this overlap. Its effect would necessarily be to 
widen the channel of communication between the gulf of Ap- 
palachia and the open western sea. This view is strengthened 
hy the fact that the lower division of the shale retains its full 
thickness of about three hundred feet quite to its extreme west- 
ern edge, showing no sign of the proximity of the shore. 
Furthermore, the remarkable outliers at Bellefontaine, 
which form the summit of the state of Ohio at a hight of 1500 
feet above tide, show positively that at some time during the 
shale period that point was under water. These scanty expos- 
ures do not at present allow a determination of the precise date 
of the deposit, but, considering the great erosion which has 
taken place, it is reasonable to conclude that the lower shale 
was present and that the remaining fragments belong to that 
division.* 
On the western side of the arch the same shale continues, but 
there it rapidly thins down, so that in the counties near the falls 
of the Ohio, in Indiana, it does not exceed fifty feet in thick- 
ness. The few fossils, however, that it has furnished indicate 
its relationship, in part at least, to the lower portion of the Ohio 
shale and to the Genesee of Xew York."!' 
^* The present great hight of these outliers indieatesconsiderable subsequent 
elevation. Indeed, there are some reasons for believing that this elevation is 
still in progress. 
t Geol. Surv. of Indiana, 1874, p. 126. 
