Aug. 13, 1917 



Origin of Alkali 



335 



rock are leached out and concentrated in the surface soil. Leaky irri- 

 gation canals and the rise of the ground-water table give greatest and 

 quickest concentrations. 



GEOLOGIC FORMATIONS 



Field studies were made of the area during the years 191 3 and 1914, 

 when some 400 representative samples of sandstone, shale, alkali, clay, 

 and ash^ were collected and later submitted to complete "alkali" 

 analysis. The data of the nitric and potassium content have been 

 presented and discussed elsewhere (9, 10). 



The geological evidence shows that during the Cretaceous and the 

 Tertiary periods shallow seas covered the eastern part of Utah, western 

 Colorado, western Wyoming, eastern Idaho, and extended north through 

 Montana into Canada (9, map). This is not the whole area covered, 

 but the part given special study in this paper. The Lower Cretaceous 

 is wanting, and the Upper Cretaceous lies unconformable on the Jurassic 

 deposit. The climate during the Jurassic was arid, as is evidenced by 

 the great areas of red sandstone containing rock salt and great quanti- 

 ties of gypsum. During the Lower Cretaceous the area was land and 

 suffered erosion. The divisions of the periods in general are as follows: 



Arrangement of geologic formations 



i Light-colored sandstone, lime- 

 f Green River for- stone, and shale with beds of 



Tertiary Eocene. 



Upper Cretaceous. . . 



m a 1 1 on, 



satch, 



Union. 



Montana Mesaverde. 



Wa- 

 Fort 



Colorado . 



(Dakota. 



° I rhyohtic ash and lenses of 

 " ( salt and gypsum. Coal beds 

 and layer of dark-colored 

 shale. Forms floor of Uintah 

 Basin. 



Alternating layers of buff 

 sandstone and shale with 

 beds of workable coal near 

 base. 



Black and blue-gray shale 

 with light-colored sand- 

 stone near top. 



Buff sandstones, highly col- 

 ored shale with carbonace- 

 ous shale and some coal at 

 the base. 



2,000-4,000 feet in 

 thickness. 



1 ,000-3 .000 feet in 

 thickness. 



300-2,500 feet in 

 thickness. 



Unconformity. 

 Jurassic 



{Brown-, yellow-, and red-colored sandstone with lenses of lime- \500-2.000 feet in 

 stone and gypsum. / thickness. 



When the sea again covered the land at the end of Lower Cretaceous 

 times, conglomerates, sandstone, and shale were deposited; and during 

 the Upper Cretaceous the sea continued to deepen during the period of 

 deposition. But at times the sea was shallow, forming layers or salty 

 marshes in which gypsum and salt were deposited. The shales of the 

 Mancos, which are more than 2,000 feet thick in places, contain beds 

 which are heavily impregnated with gypsum, sodium sulphate, and some 

 sodium chlorid. The deposit is not uniform, but appears in certain beds 

 irregularly distributed through the deposit. 



1 A term which was chosen to apply to a mixture of dry dust with crystals of alkali found just underthe 

 clay crust on the most affected parts. 



