METHODS OF WORK 291 



In the case of the Uintas, lithologic distinctions in the Mesozoic and 

 more recent beds were sufficiently persistent to permit a ready tracing of 

 the structure, especially in the eastern part of the range, where the anti- 

 clinal arch is lower and has been more completely denuded of its Tertiary 

 covering. This is not the case, however, with the Paleozoic beds; for, 

 although the west end of the range, which we first visited, is separated 

 from the Wasatch by a covered gap only 10 or 15 miles in width, it is 

 practically impossible to trace there the lithologic succession of beds 

 below the Weber quartzite observed in our key-section in the latter range. 



Our first visit to the Uintas, at the close of the field season of 1869, 

 was curtailed by shortness of provisions, due to the forced abandonment 

 of our wagon soon after leaving Provo valley, and when we finally reached 

 the valley of the Duchesne, which was the eastern limit of that season's 

 work, it was found impossible to ascend the canyon above the forks be- 

 cause of beaver ponds, which were impassable to our animals. We were 

 therefore obliged to abandon its exploration and climbed Ehodes spur, on 

 its western side, in order to reach the summit of the range at Bald moun- 

 tain, from which we shaped our course westward again. 



The field work of 1871 was carried on from Fort Bridger, on the 

 Tertiary plains to the north of the Uintas, as a supply camp, from which 

 two trips were made across the range to its southern flanks; but the 

 necessities of the work did not justify going so far west again as the 

 main Duchesne river, and thus a considerable gap was left between the 

 two seasons' field work at the very point where the best and most contin- 

 uous Paleozoic exposures are to be found. 



When, in the winter of 1874—1875, the working up of our material 

 was so far advanced that we could draw in the geological outlines on the 

 Green Eiver sheet, there was a question as to what color should be given 

 to the great quartzite core of the Uintas. Its estimated thickness 

 amounts to about 12,000 feet. Above it is an uncertain thickness of 

 beds, largely limestones, with some siliceous members, the fossils collected 

 from which were determined by the paleontologists to be decidedly 

 Upper Carboniferous, and for the most part rather high in that forma- 

 tion. In his one trip into the interior of the range, when he had climbed 

 mount Agassiz at the head of Bear river, Mr King had collected from the 

 talus slopes of that peak a well preserved Upper Carboniferous Productus 

 in Uinta quartzite. 



In the typical Wasatch section, as shown in Weber canyon, there are 

 5,000 feet of Carboniferous quartzites, with 2,000 to 2,500 feet of cal- 

 careous and argillaceous Carboniferous beds above them, and about 9,000 

 feet, mostly limestones of Carboniferous, Devonian, and Silurian age, 



