Se ee eee eS EN NOS Sage Tas S- es 
Condition of the Earth’s Interior.—Mountain- Making. 7 
and this could not have been, except through seven miles of 
local contraction along the region; but such an open space, of 
place. And, moreover, such open spaces, of no less extent, 
must have existed, in one or more ranges, underneath all conti- 
nental borders. This is proved, and, at the same time, the 
extreme improbability of their existence demonstrated, by the 
facts reviewed beyond. 
If the matter beneath was not aerial, then liquid or viscous 
rock was pushed aside. This being a fact, it would follow that 
there existed, underneath a crust of unascertained thickness, a 
sea or lake of mobile (viscous or plastic) roek, as large as the 
sinking region; and also that this great viscous sea continued 
in existence through the whole period of subsidence, or, in the 
case of the Alleghany region, t rough all Paleozoic time—an 
era estimated on a previous page to cover at least thirty-five 
millions of years, if time since the Silurian age began embraced 
fifty millions of years. 
The under-Appalachian fire-sea, if a reality, must hence have 
had a long continuanc 
But, on the above condition, it could not have begun its 
me. LKarlier, great subsidences were involved in the de- 
gpg later than the period of disturbance closing pre-Silu- 
; : 
. a 
ridge, Adirondacks, and the Archeean heights farther north 
Were made; and the under-crust sea would have been, through 
