GRIMSLEY. | Origin of Gypsum. 81 
In the southern part of the state, after the central area had 
been raised into land, shallow water conditions prevailed. 
Thick deposits of shales were laid down, interrupted for a 
time while the massive gypsum was deposited. The gypsum 
has no clay seams in it, and is compact and pure. This inter- 
ruption appears strange and difficult to explain. It may have 
been due to some climatic change whereby the rainfall was 
lessened, and so the erosion and amount of sediment carried 
into the gulf would be checked. Again, there may have been 
land movements lowering the surrounding land, and the ero- 
sion and transportation of sediment thereby stopped. 
In the western part of Barber county there were two gypsum 
deposits, separated by shales. The conditions after the forma- 
tion of the Medicine Lodge gypsum were apparently similar to 
those before, and red shales were again deposited. The appear- 
ance of the shales above and below the gypsum to-day is dif- 
ferent. The shales below are bound together by the selenitic 
network which has been formed by solution of the gypsum layer 
above and adeposition below. This action is without doubt go- 
ing on to-day. Inthe shales above the gypsum this feature is 
absent. 
Origin of the Secondary Gypsum Deposits. 
The deposits of earthy gypsum in the central part of the state 
were formed at a much later time than the rock deposits we 
have been describing. They occur in low swampy ground and 
strong springs of gypsum water occur in nearly all of them. 
At the same level or 10 to 20 feet below the earth is a stratum 
of solid gypsum, while near most of these deposits no gypsum 
is found above. Near the bottom of the Rhodes deposit Dr. 8. 
Z. Sharp found recent shells of genera Planorbis and Physa, 
and an Indian spear-head was also found. Similar shells were 
found by the writer, in the Longford earth near the bottom of 
the deposit. In the earth south of Dillon bones and shells were 
found. 
Gypsum in a form resembling satin spar and in an earthy 
form is deposited at the present time in dry weather to the ex- 
tent of a half inch in a few days by the evaporation of running 
