412 
CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1902. [bull. 213. 
It will be seen that both materials are very pure gypsum, and that there is no 
apparent reason why the Virginia material should not be as satisfactory as that 
from Kansas. 
The calcination of the product is usually carried on in small vertical kilns closely 
resembling those which are in common use for lime burning. These kilns are 
charged with alternating layers of fuel (usually coal) and lump gypsum. Small 
rotary kilns have been used experimentally, but have not proved successful, as the 
calcined product from a rotary kiln is discharged in small fragments, which can 
not be treated satisfactorily in the alum bath. After burning to a red heat, the 
gypsum is submitted to the action of a 10 per cent alum solution. It is then recal- 
cined, and finally ground in emery mills. 
The product is a very fine-grained white powder. On the addition of water 
this cement hardens, but the hardening is slow, relative to that of other plasters. 
Another peculiarity of the material is that, even after the hardening has com- 
menced, the partly set cement may be reworked with water and will take its set 
just as satisfactorily as if the process (of hardening) had not been interrupted. 
By far the largest openings of the district are those at Plasterco 
post-office (Gypsum station), a mile or so southeast of Saltville. The 
gypsum mines at this point are worked by the Buena Vista Plaster 
and Mining Company. The bed now worked is about 30 feet thick, 
dipping northwestward at an angle of 50 degrees or more, and has 
been mined to a depth of 280 feet. The shaft at present used is 180 
feet deep. Part of the product is ground for land plaster at the mill 
of the company, located a short distance from the shaft, and part is 
calcined at the same plant, the total product being about 11,000 tons 
per year. The crude gypsum is reduced to 5 inches in a nipper, and 
then to about J inch in a rotar}^ crusher, receiving its final reduction 
in a Sturtevant rock-emery mill. The material used for land plaster 
is then sent to the bagging machines, while that to be calcined goes 
to the kettles. A certain amount of wall plaster is also made at this 
plant, by the addition of retarder and hair to the calcined plaster. 
Analyses of crude gypsum from the mines of this company follow: 
Ancrt uses of gypsum from Plasterco post-office, Va. 
Constituent. 
Lime 
Sulphuric acid 
Water 
Magnesia 
Baryta 
Alumina and iron 
Silica 
33. 20 
46.04 
19.40 
.70 
.10 
2. 
33. 20 
44.74 
20.85 
.05 
.19 
.46 
.49 
33. 00 
47.14 
19.07 
Trace. 
Trace. 
0. 55 
.02 
31.82 
40.24 
21.30 
1.75 
1.10 
1.95 
1.68 
1. Crude rock, as mined. P. de P. Ricketts, analyst. 
2. Crude rock, as mined. Henry Froehling, analyst. 
3. Ground rock, for land plaster. P. de P. Ricketts, analyst. 
4. Ground rock, for land plaster. Henry Froehling, analyst. 
THE SALT INDUSTRY. 
Although indications of salt appear at several points in the region, 
the salt industry is at present confined to the immediate vicinity of 
