REVIEWS 449 
In the Carboniferous the clays underlying the coal seams have been utilized in 
the manufacture of pottery and firebrick at several points. Other Carboniferous 
shales are adapted for use in manufacturing vitrified and pressed brick and terra-cotta. 
The lowermost division of the Cretaceous—the Tuscaloosa formation — carries 
important clay deposits. The strata composing the Tuscaloosa are prevalently yel- 
lowish and grayish sands, but subordinated to these are pink and purple sands, 
thinly laminated dark gray clays with leaf impressions, and great lenses of massive 
clays varying in quality from pure white-burning clays to dark purple and mottled 
clays high in iron. The Tuscaloosa occupies a belt of country extending from the 
northwestern corner of Alabama, where it is thirty or forty miles wide, around the 
border of the Palzozoic area to the Georgia state line at Columbus, where it is only a 
few miles in width. East of the Alabama river the proportion of clay to the rest of 
the strata is less than west of that river, and the clays themselves are more sandy. 
The purest clays are found in Fayette, Marion, Franklin, and Colbert counties. The 
clays above described have been long used for stoneware and pottery. 
Fire clays are abundant in the lower Claiborne -division of the Tertiary, in 
Choctaw, Clarke, and Conecuh counties. The Tertiary and post-Tertiary clays have 
not, however, been investigated in much detail. 
Over the greater part of the coastal plain, in the river “second bottoms,” yellow 
loams occur which are used for the manufacture of common brick. Lenses of pure 
plastic clays are also found in many places interstratified with Pleistocene sands. 
In the third section Ries discusses the qualities requisite in clays designed for 
different uses, and gives detailed records of the tests and analyses of seventy-two 
Alabama clays. 
SLosson, E. E., AND Moupy, R. B. The Laramie Cement Plaster. Tenth 
Ann. Rept. Wyoming College Agri. & Mech, Igoo. 
The Laramie cement plaster is made from gypsum obtained a short distance 
south of Laramie, Wyo. The Triassic beds of the region contain much gypsum, one 
particular stratum of considerable thickness occurring near the base of the Trias, 
about two hundred feet above the Permian sandstone. The disintegrated gypsum 
from the outcropping edges of these beds has been washed down and redeposited in 
depressions in the plains. These gypsite deposits contain a considerable percentage 
of impurities, chiefly silica and lime carbonate. The Laramie gypsite bed has an 
average depth of about nine feet. he upper seven feet is pure gypsite, underlain by 
a “red layer” five inches thick, below which is a foot or more of gypsite resting on 
gravel and clay. 
The Laramie cement plaster is made by the kettle process, the temperature being 
carried to 380-390° F. An analysis of it showed: 
Ultimate, Probable Combinations. 
SiO, 5.50 CaSO, Tie 
Al,O, 0.59 CaCO, 7.86 
CaO AG) ak CaO 2.35 
MgO 1.45 MgCO, 3.04 
SO; 43.37 Si0 2 5.50 
CO, 5.05 Al,O, 0.59 
H,O 6.93 H,O 6.93 
The dehydration is evidently not carried far enough. Experiments show that the 
common cactus (Opuntia platycarpia) and malva (Malvastrum coccineum), when dried 
and ground, form cheap and satisfactory retarders. Tests for tensile strength show 
that all retarders decreased the strength of the plaster. 
