VALLEY REGION ; ORIGIN OF THE ROCKS. 189. 
Silurian 5,000 feet ; Devonian 100 feet ; Carboniferous 6,500 
feet, making in all not less than 21,600 feet. 
We must next endeavor to explain how these beds have 
been elevated above the sea so as to become a part of the dry 
land, and how they have been brought into the positions 
which they now occupy. As originally deposited, we may 
infer that they were spread out upon the floor of the interior 
sea in sheets or strata, which, allowing for the slopes and 
inequalities of the sea bottom, and the greater thickness of 
the deposits near the shore, were in approximately horizon- 
tal position, and if they were brought up above sea level by 
some gradual and uniform motion of elevation, we should 
have a condition of things such as prevails in the lower part 
of this State, in the territory made by the newer formations 
Cretaceous and Tertiary, viz., the beds thus elevated would 
be nearly hi rizontal, but with a slight slope or dip towards 
the sea, or towards the northwest; there would be no 
mountains or great inequalities of surface except such as 
might be produced by the ero.ion of rains and running 
waters, and at any one place only a very few feet in thick- 
ness of strata could thus be exposed. We also see to the 
northwest of the region with which we are here concerned, 
in Alabama, Tennessee, Kentucky, and beyond, approxi- 
mately level or horizontal strata into which erosion has cut 
only a few hundred feet, aud exposed only a few hundred 
feet of the uppermost beds. On the other hand, we notice 
running diagonally through the upper half of Alabama and 
thence northeastward thruugh the other States to Canada, 
a belt of country perhaps to 150 to 200 miles in width, the 
strata of which are seldom in horizontal or even approxima- 
tely horizontal position. They are inclined to the horizon at 
varying angles, being sometimes even perpendicular; their 
outcropping edges may be followed for many miles in a 
northeast direction; the lines of outcrop of the edges of 
different beds are approximately parallel with each other, 
and by crossing over these outcrops in a direction at right 
angles to their trend, i. e., from southeast to northwest, we 
may pass in succession over the strata of the whole series 
of geological formations from Cambrian up to Coal 
Measures, and all within the distance of a few miles. A: 
