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_Geological Survey of Alabama.--Bulletin 4._ By =C. Willard Hayes=.
(Report of the Geology of Northeastern Alabama and Adjacent
Portions of Georgia and Tennessee).
This report covers an area of 5950 miles, two-thirds in Alabama.
Topographically it falls into three divisions: 1) the Cumberland
and other plateaus of the northwest; 2) in the center, anticlinal
valleys--Browns and Wills, with the synclinal mountains--Sand and
Lookout; 3) the monoclinal mountains, the "flatwoods" (Coosa shales)
and the chert hills (Knox limestone) of the southeast. The drainage of
the first is radial from the center of the plateau to the Tennessee;
that of the second, once consequent upon the folded structure, is now
adjusted to the strike of the soft beds.
The formations are Cambrian, Silurian, Devonian and Carboniferous.
Total thickness is from 13,000 to 18,000 feet in the east, but
decreases westward. Hard sandstones of the Carboniferous form the
cappings of the plateaus and synclinal mountains. In the anticlinal
and monoclinal valleys the Silurian and Cambrian appear. The rocks
pass from the nearly horizontal beds of the plateau region, by narrow
unsymmetrical anticlines with steeper dip on the northwest side, and
by broad shallow synclines, to the complicated folds of the southeast.
The axes of these latter folds dip more or less abruptly northward and
southward, causing the ridges to assume zigzag courses. Synclines are
often crossed by anticlines.
Thrust faults exist, some of great magnitude, and traceable for 200
to 300 miles. By the "Rome thrust fault" the Cambrian shales have
been shoved four to five miles over upon the Carboniferous shales.
Most of the overthrust strata have been worn away, but tongues of
Cambrian shale still remain to all appearances lying conformably upon
the Carboniferous strata. Transverse thrust faults terminate Gaylor's
ridge, Dirt Seller Mountain, and Lookout Mountain on the south.