66 CEMENT MATERIALS AND INDUSTRY. [bull. 243. 
have been in operation in supplying material for tile works and pot- 
teries. The clays lie near the base of the formation, close above the 
black shale of the Devonian, and average about 40 feet in thickness, 
though in places they reach '200 feet. The clay beds alternate with 
seams of chert which are from 2 to 8 inches in thickness, while the 
clay beds vary from 12 to 18 inches. The upper half of the clay is 
more gritty than the lower half, which often contains material suitable 
for the manufacture of the finer grades of porcelain ware. Analyses 
3-6 in the second table on page 70 show the composition of several vari- 
eties of clay from this section. 
PENNSYLVANIAN (" COAL MEASURES") SHALES. 
In this group are numerous beds of shale which have been utilized 
in the manufacture of vitrified brick and fire brick, but many of them 
will probably be adapted to cement making. A great body of these 
shales occurs in connection with the coal seams of the Horse Creek or 
Mary Lee group, in Jefferson and Walker counties, and in position 
where they are conveniently situated with reference to limestone and 
coal and also to transportation lines. They are therefore well worth 
the attention of those contemplating the location of cement plants. 
On the property of Mr. W. H. Graves, near North Birmingham, 
overlying the coal seam mined by him, are two beds of shale — one 
yellowish, the other gray. These two shales have been tested and 
analyzed, and their composition is shown in Nos. 1 and 2 of the second] 
table on page 70. 
Similar shales are used also at Coaldale, in Jefferson County, and aJAj 
Pearce's mill, in Marion. Of these we have reports of physical tests, | 
but no analyses. 
So also most of the coal seams mined in Alabama rest upon cla} 
beds which have not as yet been specially examined as to their titnesi 
for cement making; but, in view of the proximit}^ of the coal mines U\ 
the limestones, it might be worth while to investigate these underclay 
of the coal seams. 
CRETACEO US CLA YS. 
In many- respects the most important formation of Alabama wit! 
regard to clays is the lowermost division of the Cretaceous, whic 
lias been called the Tuscaloosa, and which is, in part at least, of tlttp 
same geologic horizon as the Raritan clays of New Jersey. The pre 
vailing strata of this formation are yellowish and grayish sands, bu 
subordinated to them are great lenses of massive clay, varying in qua 
ity from almost pure-white burning clay to dark-purple and mottle 
varieties high in iron. 
The formation occupies a belt of country extending from the nortl 
western corner of the State around the edges of the Paleozoic forms 
tions to the Georgia line at Columbus. Its greatest width is at tUfe 
