GRIMSLEY. | History and Distribution. 27 
2 to 70 feet below the surface. The upper bed is to 8 feet 
thick, and is separated by a 1-foot seam of soft shale from the 
lower 12-foot ledge. Five companies are engaged in the plaster 
manufacture at this point. 
In the eastern part of the state, near Alabaster Point in losco 
county, a large deposit of gypsum is worked. At the quarry 
of the Western Plaster Works the rock is 20 feet thick, and of 
fine quality. The Michigan deposits are Lower Carboniferous 
in age, and a very large portion of the gypsum rock is ground 
for land plaster or fertilizer. The production commenced about 
1856, and the manufacture of plaster of Paris began in the 
Sixties. 
Gypsum in Virginia.° 
The gypsum deposits of Virginia are found in the southwest- 
ern portion, in Smyth and Washington counties especially. 
Near Saltville the rock is nearly 600 feet thick. It is stated 
that the amount must be estimated in square miles rather than 
acres. Up to present time the output has been small, amount- 
ing to some 6000 tons. 
These eastern and central deposits belong to the earlier part 
of the Paleozoic era of geological time. In the west central 
region of the Mississippi valley occur valuable gypsum deposits 
which are more recent and belong to the closing part of the 
Paleozoic and Mesozoic time. The rock is found in lowa, Kan- 
sas, Arkansas, Oklahoma, Indian Territory, and Texas. 
Gypsum in Iowa.!° 
The gypsum deposits of commercial value in Iowa are found 
in Webster county in the north central portion of the state, in 
the vicinity of Fort Dodge. They were first described by Owen 
in 1852, and the mineral was described later by Worthen and 
others. The area covered is nearly fifty square miles, in the 
shape of an irregular triangle or rectangle, and the gypsum 
trends northeast and southwest nearly at right angles to the 
valley of the Des Moines river. ‘Topographically the area is 
9. Resources of Southwest Virginia, Boyd, pp. 104-108, 1881. 
10. Iowa Geological Survey, Vol. III, Keyes, pp. 260-304, 1895. 
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