. 
. 
if 
1872.] 455 [Lesley. 
proves that the laterally acting energy (whatever may have been its origin) 
was acting ona great plate of Paleozoic rockmass, at least (counting in 
the coal measures) fowr miles thick ; solid, although flexible, itself ; but 
free, when broken, to slide on its foundations, as the broken up flakes of 
ice slides over the water which supports them. 
That there was no absolutely fluid (lava?) underground beneath them 
is evident from the total absence of volcanic rocks at the present eroded 
surface, along these faults, even when the uppermost Sudsilurian rocks 
appear in one wall. (The numerous warm springs connected with the 
Virginia faults are explicable on chemical principles, no doubt.) But be- 
neath the uppermost Subsilurians are vast formations, all more or less 
metamorphosed, and many converted into granites and other crystalline 
forms. Here we have the plastic mass we need, over the surface of which 
(of course, an eroded surface, but, probably, eroded to a plane containing 
no Alpine or even Subalpine inequalities) the Paleozoic deposits, consoli- 
dated by time into a consistent, but never yet dried, sheet, seven miles 
thick in Pennsylvania, five miles thick in Virginia, three miles thick in 
Tennessee, moved with a certain freedom, under a lateral pressure, from 
the southeast, at the close of the Coal Era. 
I have formerly taken occasion to ascribe the difference of effect ex- 
hibited by this pressure in Pennsylvania and in Tennessee to the differ- 
ence in the thickness of the Paleozoic mass. In Pennsylvania it was 
folded ; in Tennessee dislocated. But the difficulty which pressed on 
Mr. Rogers to explain the sustentation of the vaults of our Northern an- 
ticlinals, is encountered equally by the Southern geologist who will explain 
the stable equilibrium of his tilted prisms. 
To return from this digression to the cross fissures, which cut off the ends 
of the Chilhowee and other mountains (and an example of them is given 
in my map of Bompas Cove), it must be understood that they do not obey 
one law, as do the principal and parallel dislocations of the country. 
They sometimes run square across from one of these to or towards 
another ; seldom cutting a prism entirely off; usually cracking its north 
western edge fora certain distance into its body. It is a subordinate and 
secondary system of faults. But by means of it most of the Appalachian 
ridges or mountains, of Middle Silurian and Upper Divonian age, are 
swallowed up and ended at the surface ; just as are the mountains of 
Chilhowee sandstones, in such cases as that described by Mr. Safford above. 
The section accompanying my map will, perhaps, be compared by some 
reader of this paper with Mr. Safford’s section on page 202, and they will 
be seen to be very different. It is only needful to explain that my section 
was made with instruments on the ground under favorable circumstances, 
and carefully drawn to the same horizontal and vertical seale ; whereas 
the section on page 202 is like Mr. Safford’s other sections, drawn to a ver- 
tical scale at least twenty times greater than the horizontal, and, as he 
says, ‘‘it is not intended to be accurate in detail.’’ 
In fact nothing can be more erroneous than the impression on the mind 
