VALLEY REGION ; CHARACTERS OF THE ROCKS. 155 
of pyrite in the form of nodules or kidney-shaped concre- 
tions, the decomposition of which supplies the sulphur of 
these springs. In North Alabama the thickness of the 
Black Shale may go up as high as 100 feet, but so extreme 
a thickness is rarely seen further south. 
THE CARBONIFEROUS.—This we conveniently divide 
in Alabama into two parts, a lower, or Sub-Carboniferous, 
and an upper or coal bearing part, the true Coal Measures. 
The thickness of the latter is placed by Mr. Squire at 5525 
feet, and the former at 1,200, making a total of between 6,000 
and 7,000 feet. 
Sub-Carboniferous.—Prof. Safford divides this formation 
in Tennessee into an Upper or Calcareous member, and a 
Lower or Siliceous one. This division wili also apply 
equally well to that part of Alabama north of the Tennessee 
river, but to the south, and everywhere in the narrow anti- 
clinal valleys of the State, this division will not suit, and 
we are compelled to make a different one. Like Prof. Saf- 
ford, however, we make a two-fold division, the Fort Payne 
Chert below, and the Oxmoor Sandstone and Shales, and the 
Bangor Limestone above, roughly corresponding to the 
divisions of Prof. Safford, with the differences below 
specified. 
In the Tennessee Valley, the siliceous member of the 
Sub-Carboniferous consists of a great series of cherty lime- 
stones somewhat analogous to the Knox Dolomite, but with 
the lower part more cherty than the upper. This lower 
part gives rise to rather poor siliceous soils, and the region 
of its occurrence both in Alabama and Tennessee is known 
as the “Barrens”; the upper part of the Siliceous member 
is more calcareous and the soil derived from its disintegra- 
tion isared loam of more than ordinary fertility, well known 
in the Tennessee Valley as making the best farming lands 
of that section. Here again there is an analogy tothe Knox 
Dolomite, which affords on the cne hand rich red loam soils, 
and on the other poor cherty ridges. 
The chert of the Sub-Carboniferous is in general very 
similar to that of the Knox Dolomite, but differs from it in 
being usually very highly fossiliferous, containing the casts 
or moulds of shells that have been leached or dissolved out. 
