150 Till Ann rial II Geologist. September, ISiM 
eastward near the Lahanou Co. line after a concealment of 20 miles. 
80 large a semilenticnlar mass of sandstone intercalated in a 
group of soft strata must have had some local cause and in seeking 
this we ma}- be aided hy recalling the geograph}- of Pennsylvania 
at the time under consideration. 
Tn the early Devonian era the interior states, generalh- speaking, 
consisted of an open ocean extending from the Atlantic land on 
the east in what is now eastern Pennsylvania to an unknown dis- 
tance westward and limited to the northward by the Arcluean High- 
lands of Canada. In this palaeozoic ocean a gentle elevation was 
taking place along a line from northeast to southwest through 
Ohio, wherel)v what is now known as th<^ Cincinnati ridge or arch 
was brought into existence. Ultimatel}-, and probably before the 
Devonian era closed, this ridge partly severed the eastern portion 
of this ocean from the rest and formed the Appalachian strait or 
gulf. The continued subsidence of this strait or gulf allowed the 
deposition in it of sediment from the adjoining land on the east 
but the nature of the sediment on the area now in question would 
indicate by its fineness, being mostly sand}' shale, that the land 
was not very near, or if near not ver}' high. The latter is more 
probable. Such deposits do not indicate shallow water or strong- 
currents. The actual margin of the Appalachian gulf or strait 
has apparently been destroyed b}- the corrugation and erosion that 
have ensued, so that the present Hamilton deposits are those which 
were deposited off shore, but neither in deep water nor on the 
border of the land. 
But so great and sudden a change in the nature of the strata 
implies some great and corresponding change in the physical 
geography and especially in the attitude of the land — a change 
that would allow the Hamilton sea to assort and arrange coarse 
sand where it had previously deposited only fine shale. 
The arrangement of this sand appears to indicate a center of 
distribution from which it was spread over the whole area that it 
now occupies and it seems a not improbable supposition that this 
centre was the mouth of some large i-iver which bore into the Ap- 
palachian sea its tribute of sand and mud. The former was as- 
sorted and distributed over the region around the river-mouth, and 
the latter carried out to a greater distance where it ultimately be- 
came a bed of shale. That the ancient Atlantic land was drained 
by a system of streams goes without saying, and it may Ite that 
