150 GEOLOGICAL SURVEY OF ALABAMA. 
in that State apparently below the Shales above named, which 
he designates as the Knox Shale and Sandstone. In Ten- 
nessee the distinction between the shale and the sandstone 
member of the Knox Group, can be consistently followed 
out, but it does not seem practicable in Alabama to separate 
the two, for beds of tolerably massive sandstone occur at 
many horizons, interbedded with the shales, So also, for 
the reason that in Alabama the great masses of quartzite 
do not occur at the base of the shales, nor apparently, at 
any definite horion in the same, we have not used Professor 
Safford’s name Chilhowee to designate the rock: Similarly 
it appears necessary to adopt a distinct name for the thin- 
bedded limestones with clay seams, of our “Flatwoods,” 
since they play a very subordinate part if they occur at all 
in Tennessee. As above intimated, the Weisner Quartzite 
makes no show in any of the region covered by this map, 
and it is mentioned here only to give completeness to our 
enumeration of the Cambrian rocks. 
THE SILUBIAN.—We have not yet in Alabama found it 
practicable to arrange our Silurian strata in more than three 
principal divisions, which, beginning at the lowest and com- 
ing upwards, are as follows: Knox Dolomite, Trenton or 
Pelham Limestone, and Red Mountain or Clinton. 
Knox Dolomite.—This name has been given by Dr. Saf- 
ford to a series of rocks occurring in the vicinity of Knox- 
ville, Tennessee, and, inasmuch as the rocks of this horizon 
in Alabama are identical with those described by him, we 
have retained the name in the Alabama Survey. This is 
one of the most important and widely spread of our older 
geological formations and its characteristic rocks are magne- 
sian limestones or dolomites, sometimes quite pure, but 
more often impregnated with siliceous matter. This sili- 
ceous matter is sometimes found asasandy impurity in some 
of the dolomites, upon the weathering of which it becomes 
quite prominent. For this reason, many of the dolomite 
beds of the lower part of the Knox Dolomite, when exposed 
to the weather, show a rough sandy surface, marked by shal- 
low cracks running in every direction as if the rock had been 
hacked with some cutting instrument. These purer and 
sandy dolomites, together with some beds of tolerably pure 
