148 GEOLOGICAL SURVEY OF ALABAMA. 
a coarse grained sandstone or conglomerate, which in the 
valleys further westward, such as Cahaba Valley and Jones’ 
Valley, are wholly wanting. So also the shales of the same 
formation are sandier in composition in the Coosa Valley 
and more calcareous in the two other valleys named. 
THE CAMBRIAN.—The rocks of this formation are con- 
glomerates, sandstones and shales in the Coosa Valley 
region, and shales and shaly limestone in the valleys which 
occupy part of the area of this map. The maximum thick- 
ness may be put at 10,000 feet, but this great thickness is 
seen only in the eastern part of the Coosa Valley, while in 
Jones’ Valley the thickness is probably Jess than half the 
above. 
The sub-divisions of the Cambrian which we recognize | 
in Alabama are, in ascending order, as follows: the Coosa 
Shales, the Choccolocco or Montevallo Shales, and, interbed- 
ded with the last named, the Weisner Quartzite. 
Coosa Shales.—In the valleys here described the rocks 
are, commencing with the lowest, thin-bedded limestones 
with clay seams between; usually very greatly contorted 
and tilted at high angles. Where these rocks come to the 
surface there results from their decomposition a very stiff 
calcareous clay soil. These lands being very level and 
hence badly drained, are not much cultivated, and in Ala- 
bama are generally known as “Flatwoods.” The town of 
Bessemer is upon one of these “Flatwoods” tracts, and 
similar areas may be seen between Bessemer and Birming- 
ham, and northeast of Springville towards Gadsden, and in 
the immediate valley of the Coosa River up to and beyond 
the line between Alabama and Georgia. The shaly lime- 
stones that give rise to these “Flatwoods,” we have called 
Coosa Shales. 
Montevallo Shales.-- Above these Coosa Shales we find a con- 
siderable thickness of sandy shales of a great variety of col- 
ors, such as olive, green, brown, chocolate, yellowish, etc. The 
original material was a calcareous shale, but at the outcrops 
the calcareous matter has mostly been pretty thoroughly 
leached out, and only the more siliceous parts left. These 
shales crumble up in places into small fragments about the 
size and shape of shoe-pegs. Sometimes they are more 
