28 University Geological Survey of Kansas. 
a nearly level prairie, with imperfect drainage, and deeply 
trenched by the Des Moines river. The gypsum beds are re- 
garded as Cretaceous in age, and rest upon the Lower Coal 
Measures, and are covered by the glacial drift. At the base of 
the gypsum is a layer of red sandy or clayey nodular shale of 
variable thickness. The character of the gypsum, as given by 
Keyes, is as follows: 
‘‘The gypsum deposits vary in thickness from 3 or 4 to 30 or more feet, the 
average measurement being about 16 feet. The gypsum is the perfectly massive 
variety, made up of numerous thin, alternating bands of white and gray ecalcic sul- 
phate, the differently colored layers measuring from one-eighth to one-half of an 
inch in thickness, and finely corrugated. The lower part of the deposit, although 
not strikingly different from the upper portion, often contains some impurities, 
and on this account this part is usually ground into land plaster, while the upper 
portion is made into stucco. The gypsum beds appear to be thoroughly erystal- 
line throughout, the individual crystals being columnar or needle-like, arranged 
closely together with their long axes at right angles to the sedimentation planes. 
This arrangement seems to be uniform throughout the entire deposit.”’ 
Well borings seem to show a considerable extension of the 
gypsum beyond the limits of known outcrop, both northeast 
and southwest of the Fort Dodge district. The deposit was prob- 
ably laid down in a shallow estuary which extended out into a 
broad open sea in Niobrara epoch of Cretaceous time. The 
Iowa gypsum is used mainly for stucco or plaster of Paris and 
a small amount as land plaster. Some years ago the rock was 
used for building purposes and for flagging for walks, and the 
blocks stand without crumbling except on the surface, which be- 
comes bleached and finely cracked. Keyes has computed that 
the available supply of gypsum in this region is more than 40, - 
000,000,000 tons, and at present rate of production would last 
800,000 years. The gypsum is easily quarried and transporta- 
tion facilities are good. The product is shipped north, west, 
and south, and the land plaster is sold mainly in Wisconsin. 
Gypsum in Indian Territory and Texas. 
To the southwest, in Indian Territory and Texas, large de- 
posits of gypsum occur. Marcy’s Red River Report” in 1852 
states that near the source of that river the waters have a pe- 
11. Pages 52, 91, 172, 173. 
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