Devonian Era in the Ohio Basin. — Claypole. 101 
York and even Pennsylvania, but its main effects were felt in 
the northeast, and it was from this region that the tributary 
sediments were poured into the gulf during the whole of the 
later portion of the Devonian era and far into that which fol- 
lowed it. The great estuary of New York was the inlet 
through which the wash of the land was brought in ; here it 
was borne back and forth by the currents and tides until it was 
thoroughly sorted and sifted and deposited, according to its 
degree of fineness, in the catch-pit outside, where those cur- 
rents were finally lost. 
The estuary itself must have shared in the elevatory pro- 
cess and, in consequence of this, the coarser part of the earlier 
deposits was eroded and carried out farther and farther to sea 
during each succeeding period, so that a great part of the 
shore-history of these sub-periods was destroyed and ultimate- 
ly accumulated in the later beds. This is probably the chief 
cause of the enormous accumulation of sand in the Catskill 
and subsequent periods and its comparative scarcity in the 
strata that represent the preceding Chemung and Portage sub- 
periods. 
But, as the close of the Devonian era approached, there 
came on a great change in the condition of Appalachia. Dur- 
ing the Corniferous and Hamilton less change occurred, the 
elevatory force having apparently spent itself. But now. in 
the time of the deposit of the upper shale, a reverse movement 
set in and the whole of this uplifted area was again depressed 
to so great an extent that it is almost certain that the Cincinnati 
promontory ceased to exist, and if any trace of it remained, it 
must have been only the two ancient islands of Nashville and 
Cincinnati, and a wide and open sea once more extended over 
Appalachia. In this sea continued the deposition of black shale 
which marked the later Devonian era in Ohio. In Kentucky 
and Tennessee it overspreads all the earlier formations with a 
sheet of material only fifty to one hundred feet in thickness — 
the Chattanooga black shale. West of the now sunken anti- 
cline it covered the Indiana slope in the same way, and is there 
known as the New Albany black shale ; while farther west its 
special characters are lost and it is merged in the indivisible 
calcareous Devonian of the Mississippi valley. 
