Devonian Era in the Ohio Basin. — Claypolc. 25 
until we reach the western slopes of the central basin that we meet 
with it again.'' 
It thus appears, whatever may have been the condition of 
the southern end of the Appalachian channel during the de- 
position of the Clinton strata, there can be little doubt that in 
the Niagara period it had been closed by the uplift occurring 
in that region, and had been converted into a deep embayment 
which may be called the Appalachian gulf. 
Another line of evidence must not be neglected in follow- 
ing up this argument. It is that in thus tracing the Clinton 
and Niagara strata away from their typical region both rapid- 
ly change their character. 
As far as they are found in Ohio, both retain their calcar- 
eous nature and are pure limestones, the older calcareous and 
the younger dolomitic. But neither of them long holds this 
tvpical composition after passing on to the southward. In the 
quotation from Shaler just given he said that the Niagara sec- 
tion increases in depth as we pass to the southward. But he 
adds (he. cit.) : "As we go southward the cherty structure 
is greatly diminished." "In east Tennessee the beds are very 
much thicker than in central Kentucky and contain a large 
amount of coarse sediment principally thin-bedded sandstone 
and at the top a true conglomerate/' ' Again (p. 394) he adds: 
"The Niagara limestone is only distinctly marked in certain 
parts of the state and is generally quite thin." 
The obvious deduction from the above quotation confirms 
the conclusion at which we arrived from the consideration of 
the outcrop of the same strata, that the shore-line was not far 
distant to the southward and that, whatever may have been the 
condition of the area during the Clinton period, it had become 
before the Niagara had far advanced, a closed gulf, the only 
connection of which with the open ocean to the westward, was 
around the northern end of what had become the Cincinnati 
promontory, or headland, in northern Ohio and Indiana. 
The evidence that can be deduced from the Lower Helder- 
berg group as it is developed in the region of southern Ap- 
palachia strongly confirms the reality and the persistence of 
the series of changes which have been outlined above, the 
closure of the Appalachian channel and its subsequent contrac- 
tion of the continuance of the great southern uplift. Begun 
between Ordovician and Silurian days, to it is probably due 
