86 KANSAS ACADEMY OF SCIENCE. 



of a large basin, shallow except in the area where the deposit was 

 formed, and to suppose that as the water was concentrated it retired 

 into the deeper part, and that the salt already deposited was washed 

 down with it. ' 



Or the water might have been supplied by flowing in over a bar at 

 a rate about equal to that of evaporation. Some water must have been 

 furnished by the streams which carried in the clay that is found in 

 irregular layers in the gypsum, but, unless there was some source of 

 gypsum aside from sea-water, these streams would add very little to 

 the amount of gypsum, and they would increase the amount of water 

 to be evaporated. 



In whatever manner we suppose the water to have been sujjplied. 

 the real difficulty in the way of the evaporation theory is that of ac- 

 counting for the concentration of such enormous amounts of water 

 within a comparatively short time. The depth of two miles given 

 above for the inland sea is for a layer of rock gypsum only eight feet 

 thick ; and as the total thickness in many places is at least four or five 

 times as much, besides an unknown amount taken away by erosion, 

 the water evaporated during later Permian times cannot have been 

 much less than the equivalent of a sea eight or ten miles deep over 

 the area where the heavy deposits of gypsum are, or where they have 

 been removed by erosion. 



In order to produce the necessary concentration, the surface of the 

 gypsum sea must have been subjected to a dry climate ; but the pres- 

 ence of mud and sand is evidence that the neighboring land was not 

 so arid as the hypothesis seems to require. There is very little evi- 

 dence that an inland sea of any great size existed in that place in 

 Permian times. The hypothesis of an inland sea seems to have very 

 little foundation except the hypothetical evaporation of water for the 

 formation of gypsum and salt beds. There is no great unconformity 

 such as must have resulted if the land to the west had been extensive 

 enough to produce the necessary climatic conditions. "The Colorado 

 plateau was a sea bottom continuously, or nearly so, from the begin- 

 ning of the Carboniferous to the end of the Cretaceous.*'^ If an in- 

 land sea of any great extent had existed in Kansas, Oklahoma and 

 Texas during Permian times, and had been surrounded by a sufficient 

 area of land to produce such evaporation, there would be a general 

 absence of Permian rocks in the mountains west of the gypsum area. 



If we accept the evaporation theory, the existence of different lay- 

 ers of gypsum alternating with other rocks requires us to suppose 

 that the crust movements were extremely complex. We must sup- 

 pose that inland seas were formed many times in succession in the 



3. Le Conte, "Earth Crust Movements and their Causes," Smithsonian Report, 1896, p. 239. 



