JURASSIC BEDS 23 



quantities it apparently originated from materials de- 

 posited from concentrated solutions in some ancient sea. 

 The deposits in the areas studied were made during Cre- 

 taceous and Tertiary times which seemed to have been 

 influenced by arid climatic conditions. This area in- 

 cluding the pastern part of Utah, the western half of 

 Colorado, and the southwestern part of Wyoming was 

 covered with water during upper Cretaceous times leaving 

 the Uintah anticline as an island. 



A description of the method of formation of these shales 

 and sandstones that are so high in soluble salts is given 

 as follows (17): 



" Jurassic Beds. -The Jurassic beds contain highly 

 colored red, yellow, gray, green, or blue shale and sand- 

 stone ranging from fine grain to coarse grits. In the 

 upper members of the deposit are often found thin lenses 

 of limestone and an accumulation of gypsum. The ac- 

 cumulation and position of the gypsum beds would seem 

 to indicate that they had resulted from precipitation from 

 the water of isolated brackish lakes. 



"At the end of Jurassic times the inland sea, in which 

 the Jurassic deposit accumulated, disappeared and the 

 area was subjected to erosion. This probably took place 

 during lower Cretaceous times. Later the section was 

 again covered with an inland sea and deposits were laid 

 down unconformably on top of the Jurassic. 



"These belong to the Dakota beds, the lower part of 

 which were composed of conglomerates and coarse sand- 

 stones, above which are carbonaceous shales and some low- 

 grade coal, overlain by more sandstone and highly colored 

 shales. Above the shale are found thick beds of light- 

 colored sandstone, shales, and dark-brown sandstones. 



"At about the end of the Dakota period there seems to 



