The MaTcing of Pennsylvania. — Clayx>ole. 229 
of early palaeozoic date. It may therefore be taken as evidence 
that the early palaeozoic sea extended over that area. The 
absence of every sign of later rocks is at least an indication 
that they were not deposited and therefore that later seas 
did not cover that part of the state. The existence of the 
South mountain as a barrier between these two areas 
may be quoted as an additional argument in the same 
direction. The onset of a time of enormous erosion of 
siliceous material whose only discoverable origin, though 
now altogether efifaced by erosion, must lie somewhere 
in this region and its deposition as the massive Medina sand- 
stone again points to an elevation of this portion of the 
state in mid-palaeozoic days accompanied with a certain 
amount of folding and crumpling. It is not necessary to 
maintain that the existing South mountains are of that age 
though this is by no means impossible. Their apparently 
Cambrian strata have suffered enormous erosion and the axis 
now surviving even if of later elevation, is but a fragment of 
the mass that once existed. This range may be coeval with 
the Green mountains of Vermont and be due to the southward 
extension of the same compressing force. Both may have 
stood above the water from mid-palaeozoic time to the present 
day. Both bear all the marks of immense antiquity. 
If this view is correct we have proof in Pennsylvania of a 
paroxysm of disturbance before which the rise of the Cincin- 
nati arch in Ohio sinks into complete insignificance. The 
massive South mountains then become the relics of its eleva- 
tion and the Medina sandstone 2,000 feet in thickness a mon- 
ument to its energy and extent. But the palaeozoic geography 
was not essentially changed. Sea and land on the whole still 
occupied the same areas. 
We can pass rapidly over the remainder of the palaeozoic 
era as it was unmarked by any epoch-making events. The 
formation of sediment and its deposition in the Pennsylvanian 
sea continued through the whole Devonian era. On the top 
of the Ordivician were laid down the Medina sandstone, the 
Clinton and Onondaga sh^Jes and the Lower Helderberg lime- 
stones. On these followed the Devonian system consisting of 
the Oriskany sandstone, the Corniferous limestone and the 
thick shales of the Marcellus, Hamilton, (which includes a 
massive sandstone in middle Pennsylvania), Genesee, Portage 
