Devonian Era in the Ohio Basin. — Ctaypole. 23 
and occupying the area now composing eastern Ohio, Ken- 
tucky, Tennessee, western Pennsylvania and Virginia, with 
the whole state of West Virginia, besides some adjoining 
lands. This channel was considerably wider than it would 
now appear on the map on account of the great folding and 
compression which the region has since undergone. The west- 
ern barrier of this channel may have been formed by the two 
islands, but it is probable that during a part of the era, at least, 
they were connected, forming a continuous breakwater be- 
tween the Appalachian channel and the open sea to the west- 
ward. There can be iiq doubt that the southern portion of 
Appalachia also felt the movement and that a large area was 
elevated and perhaps remained so during the Silurian era. It 
is even possible that the southern end of the channel was closed 
early in the Silurian days. Proof of such elevation is not dif- 
ficult. Ordovician limestones now overspread the whole of 
Kentucky and Tennessee and extend into Georgia and Ala- 
bama to limits not yet full}" known. Erosion and compression 
have contracted the areas that they originally covered. Con- 
sequently the Ordovician sea was at., least equally widely 
spread. But with the beginning of the Silurian era this state 
of things had passed away. If we- allow the Cumberland sand- 
stone described by Shaler in Kentucky to represent the Me- 
dina, it alone is an indication of a shore-line at no great dis- 
tance. But beyond this the comparatively narrow areas cov- 
ered by the Silurian strata in the southern states give abundant 
and indisputable evidence in the same direction. The Appal- 
achian sea, already narrowed by the two aforesaid islands 
which shut off the Appalachian channel, was still farther con- 
tracted at its southern end. Safford. writing on the subject 
says :* — 
"The minor formations composing the Upper Silurian have always 
occupied areas more or less local, never having been continuous and 
state-wide, as we have reason to think that the great limestones already 
described once were. 
In some parts of the state, in horizons on which we should naturally 
look for these rocks and where underlying and overlying formations 
are present, not a bed is found to represent the group. In the belt of 
country skirting the western base of the Cumberland table-land this is 
notably the case, and in every ravine deep enough the outcropping rocks 
show it to be so. Along the eastern escarpment of the central basin 
* Geology of Tennessee, p. 291. 
