Lesley.] 454 [May 3, 
great width, seldom over five miles, In Mr, Safford’s Section (page 190), 
across Eastern Tennessee, from the carboniferous table-land, southeast- 
ward to the Metamorphic Azoic Mountains of the North Carolina line, 
52 miles, there are eight of these faults noted, making the average width 
of each prism (supposing no fault has been omitted) 6} miles. 
The upthrow or override of the side face of each prism against the 
prism to the northwest of it, varies from fifteen thousand (15,000) feet (as 
in the Chilhowee Mountain Fault above cited, and in the Montgomery 
and Wythe County Faults of Virginia) down to five thousand, as in the 
case of the Embreeville Fault, and others of alike kind, in the same 
range, where the bottom measures of the Chilhowee, or top measures of 
the Ocoee, Formations abut against the Trenton Limestones. 
The tilt of a prism, five miles wide to an elevation of only one mile on 
its northwest border, gives an average dip of 1 in 5, or 10°. But the tilt 
has been produced by a thrust from the southeast, violent enough not 
only to produce the tilt, and thrust the prism forward and upward, but to 
rub up the broken edges of the layers of the down-tilted next prism, and 
to rub down the broken edges of its own layers ; and, moreover, to bend 
the whole body of the prism along its northwestern limit. Consequently 
we have there dips of 45°, whereas the dips everywhere else (with trifling 
exceptions) are scarcely more than 5°. 
It may be said, therefore, if astonishment be expressed at the vastness 
of these upthrows, considering the weight of the prism, that, in fact, 
there has not been so much ipward movement after all. 
On the other hand, in the sections J have made across sets of these 
faults, in other parts of the region, and where the uptilt is of lower Si- 
lurian Limestone against Coal Measures, repeated again and again, the 
proportion of horizontal to vertical is as 5 miles to 3 miles, and a dip of 
30° pervades the entire body of the prism, and of each prism, from side 
to side. 
This is a very astonishing state of things. And it characterizes a re- 
gion of country fifty miles wide by five hundred miles long, roughly 
stated. 2 
What supports these long untilted prisms of earth-crust ? 
We cannot imagine an underground Pre-silurian topography arranged 
with such regularity, as to allow the settlement of the sections of Pale- 
ozoic series, in straight lines, hundreds of miles long, and always on one 
side, the southeastern. 
It seems to me evidently necessary to assume a (in some sense) plastic 
underground, on which these wonderfully regular prismatic rods of Pale- 
ozoic rock have been able to roll one-third over and adjust themselves. 
The alternative must be, that the vacancies (of triangular section) 
have been filled with the debris of the lower crushed edges and bottoms 
of the prisms,—a most unsatisfactory suggestion—especially unsatisfac- 
tory, because the regular over-roll of all the prisms in one direction 
