Devonian Era in the Ohio Basin. — Claypole. 79 
THE DEVONIAN ERA IN THE OHIO BASIN. 
By Edward W. Claycpole. 
PLATES XVI-XVIII. 
Part I. — Continued. 
C. GEOLOGY OF THE HAMILTON STRATA. 
In Ohio. — The single outcrop of the Hamilton rocks in 
Ohio, at Prout's Station in Erie county, has been noticed al- 
ready at sufficient length. But in order to comprehend the full 
geology of die basin, the Hamilton as developed outside of 
Ohio must be considered. 
Outside of Ohio. — It was noted earlier that the outline of 
the Hamilton sea differed very little from that of the preced- 
ing period. Certain minor differences scarcely sufficient to af- 
fect the geography have been almost entirely effaced by sub- 
sequent erosion. The Appalachian gulf retained its previous 
form and the northeastern embayment was a marked feature 
in its development. 
Hypso graphic changes. — But though no new or striking 
alteration took place in the topography, yet the change of level 
inaugurated in the Corniferous-Hamilton period continued 
after its close and indeed became more marked during the per- 
iod that followed. The depression in the bed of the Appalach- 
ian gulf, forming" a basin for the reception of the Marcellus 
shale, apparently reached a maximum in southern Pennsylvania 
and persisted undiminished ; in the more northerly portion it 
even surpassed its previous limits. Hamilton-Marcellus depos- 
its on the Pennsylvania-Maryland state-line are reported by 
Stevenson* at 800 feet, but in middle Pennsylvania they reach 
1500 feet, as, for example, in Perry county,! where they arc 
apparently at a maximum. In western New York their thick- 
ness is 1000 feet, or even 1200 feet, but west of this they thin 
out, and outside of the Appalachian gulf they rapidly dwindle 
down to about 250 feet, and in the far west, where an open sea 
prevailed and the beds are calcareous, they do not sometimes 
exceed 50 feet. 
The main feature in the history of the basin during the per- 
iod in question is therefore this settling down of its bottom over 
* Second Geol. Svrvey of Penna., T2, p. 82. 
t Claypole. Second Geol. Survey of Penna., F2, p. 88. 
