DIVISIONS OF THE DEPOSITS 419 



but there is much fossil wood, and there is one band of shale which con- 

 tains fossil leaves and insects, which implies a temporary return of con- 

 ditions under which the underlying Green River beds were deposited. 

 The beds below this band of shale, however, are very puzzling and their 

 mode of deposition difficult to explain. So it is doubtful whether the 

 lower 170 feet of this section should be placed with the Green River, 

 Uinta A, or in a separate transitional formation by itself. If we take 

 away this portion of the section it would leave only 415 feet as the thick- 

 ness of Lower A. 



The upper portion of Uinta ^^A" is somewhat fossiliferous at several 

 levels, containing remains of Uintatheres, Titanotheres, and other mam- 

 mals; also turtles and unios. Much of the best material collected by 

 Riggs came from these beds and Mr. Peterson made a valuable collection 

 from them in 1912. They are 270 feet thick. 



The total thickness of Uinta "A" is, therefore, from 685 to 855 feet 

 thick, depending on whether we place the lower 170 feet in the Uinta of 

 Green River. 



Uinta "B" is about 420 feet in thickness. In these beds there is a less 

 proportion of heavy ]-iver sandstones and more sandy shales and clays, 

 which are green, gray, and red. 



From these beds came a large proportion of the collections of verte- 

 brates made by Peterson for the American Museum of Natural History 

 and the later collections made by Douglass for the Carnegie Museum. 

 The latter Avas made from perhaps 20 or more levels, and so far as possi- 

 ble records were made, so that the fossils can be referred to their proper 

 horizons. 



Uinta "^'C^'' was measured farther to the westward, beginning about 2 

 miles east of Cottonwood Grove, on White River, near the Uinta Stage 

 Line, and proceeding in a direction west of north to the highest exposure 

 on Dead Man's Bench, about 16 to 18 miles south of Vernal. This in- 

 cluded about 1,440 feet of strata. The beds here, as in most other por- 

 tions of the deposits, were dipping at an angle of 3 degrees -or more to 

 the northwestward. Lying to the northwestward across Green River 

 were mesas and benches of Uinta deposits, apparently several hui)dred 

 feet in height and evidently lying higher geologically than the geological 

 base on which we stood. The total thickness of Uinta "C" is apparently 

 not less than 2,000 feet. 



The total measured thickness of the Uinta Group here is 2,275 feet, 

 exclusive of the 1 70 feet at the bottom. The original thickness was prob- 

 ably not less than 3,000 feet. 



