Hawortu. | | Introduction. 15 
Sea’’ of Permian time, was replaced by dry land. The elevation 
processes, however, were slow and irregular with many returns to 
former conditions, so that, as emphasized by Grimsley, the partic- 
ular area in which gypsum was being deposited one time might 
be a site of limestone or shale accumulation at a later period. 
The formation of gypsum requires the concentration of ocean 
water. This must have been brought about by the temporary. 
separation, here and there, of bodies of ocean water from the 
main ocean so that evaporation could concentrate the liquid. 
There is little evidence to show that such bodies of concentrated 
water were particularly large. On the other hand it is highly 
probable that in each individual case such inland seas or lakes 
were relatively small, so that the formation of gypsum at any 
one particular time and place may not have covered many town- 
ships in extent. At this late day it is impossible to determine 
the exact limits of such gypsum beds. Erosion has worn much 
of the surface away and may have destroyed untold quantities 
of gypsum. Percolating ground waters likewise have dissolved 
portions, as Grimsley particularly shows for the Blue Rapids 
area, and therefore we are left to surmise the former maximum 
extent of such masses from the conditions as they now exist. 
It is interesting to note the geologic succession of the various 
gypsum deposits in this great western interior region. In Texas 
they seem to be confined to the Permian. In Kansas they ex- 
tend from the lowest Permian up into and nearly through the 
Red Beds, while in Lowa they are in the Cretaceous. In a gen- 
eral way, therefore, there is a migration upward corresponding 
to one northward. But in detail the Kansas deposits are just 
the reverse, passing from the lower Permian on the north to the 
upper Red beds on the south. ‘This may imply local and earlier 
elevation into dry land conditions in the northern part of the 
state, and a later one along the southern line. The general 
geologic conditions, however, show this much more conclusively. 
The Permian rocks at the north line of the state are thin and 
belong to the lower Permian, and are immediately overlaid by 
the Dakota Cretaceous. Southward the Permian thickens, 
driving the eastern limit of the Cretacous further to the west 
