Devonian Era in the Ohio Basin. — Claypole. 27 
the main feature of the above given reconstruction will not be 
substantially altered by any allowance due to this cause. It 
is clear for the most part that the geographical development 
of the gulf of Appalachia and the progress of the southern 
uplift to which its beginning and its subsequent reduction are 
both due, followed this general course. 
The Appalachian Gulf. — From a consideration of the ac- 
companying maps, on which the history of the development 
of the gulf of Appalachia has been recorded, it will be seen 
that with the gradual advance of the southern uplift there oc- 
curred episodes of cessation and even of retrogression.* The 
Clinton of the Silurian, covering but a small area in New York, 
is thickened in middle Pennsylvania to 1500 feet. Running 
southward, as already described, its outcrop returns to the 
north and rounding the end of the Cincinnati promontory 
bends south and skirts its western slope in Indiana, trending 
so far to the west that at the falls of the Ohio the group is 
represented by but twenty feet of sandy material. From, this 
point it is seen no more on the surface within our area. 
The Niagara covers an even shorter outcrop in New York 
and is missing over all middle Pennsylvania. It reappears in 
Kentucky and Tennessee,- where its outcrop returns north and 
follows that of the Clinton around the Cincinnati promontory, 
overlapping the latter in Kentucky and Tennessee, thus prob- 
ably indicating a local subsidence. Beyond this its characters 
are lost. 
The Salina is not shown on the maps as its outcrop is not 
pertinent to the subject, though in middle Pennsylvania it is 
1500 feet in thickness and of equal mass in New York, indicat- 
ing a great local subsidence in the region. 
The Lower Helderberg, overlapping the Niagara in New 
York, enters Pennsylvania, where it overlies the Salina 
in the mid state counties and finally sinks to reappear in 
southern Ohio on the other side of the Appalachian coal fields. 
It skirts the northern end of the Cincinnati promontory, is 
apparently lacking at the falls, but again conies up in west 
Tennessee, with no outcrop in Kentucky, though it probably 
underlies the western part of the state more or less extensively. 
* The islands of Cincinnati and Nashville are marked on the map's for con- 
venience of reference, and not to indicate that all through the time involved 
they were actually insular. 
