24 The American Geologist. July ' 1903- 
from the Kentucky nearly to the Alabama line, the Black shale (De- 
vonian) rests on the Nashville formation without any intervening rock. 
On the western escarpment this is also the case at a few points, 
but generally a Niagara bed has appeared to separate the two, bearing 
above it here and there a trace of the Lower Helderberg. The Niagara 
and Lower Helderberg strata are unconformable on the Nashville and 
never covered the dome of the basin." 
From this quotation, it is evident that within the limits of 
the present Tennessee, the Cincinnati-Nashville island in the 
Clinton and the Niagara periods formed an almost or alto- 
gether complete barrier between the open ocean and the Ap- 
palachian channel. A narrow passage may at times or even 
permanently have existed between them, but the Clinton strata 
are confined to the eastern part of Kentucky, where they are 
concealed, and to east Tennessee, where they are readily 
recognized by the conspicuous dyestone ore. Passing the 
state-line into Alabama they continue along the eastern mar- 
gin of the coal-fields of that state until they sink and are lost 
beneath the Cretaceous and later deposits of the gulf shore. 
In consequence of this indefiniteness of the outline of the 
Clinton group at its southern end, it is impossible to determine 
the boundary of the Appalachian channel in that direction. 
But in the next period the evidence becomes more satisfactory. 
The Niagara limestone of New York, which is missing in cen- 
tral Pennsylvania, and is concealed or thin in Kentucky, re- 
appears in the Clinch mountain series of east Tennessee, but 
extends only a short distance to the south under the name of 
the Meniscus limestone. On the west, however, of the Nash- 
ville island it appears in full force. Regarding the former 
state, Shaler says :* — 
"The next level brings in the beds which apparently answer to the 
Niagara group, as far as can be determined from the few fossils which 
they contain. This deposit is seen at points from the Ohio river south- 
wardly to the Tennessee border. The section increases in depth to the 
southward." 
And Safford, in the work already quoted (p. 311) says 
of it :— 
'"The Meniscus limestone is eminently the formation of the western 
valley. In east Tennessee the formation is represented by the Sneed- 
ville limestone in the Powell's Mountain group and lying next above 
'he Dyestone shales. Outside the region of the Powell's Mountain 
group the formation is generally wanting in east Tennessee. It is not 
* Geology of Kentucky, vol. iii. p. 1R4-. 
