BKIDGER BASIN. 239 



northward from the base of the Uinta Eange at an angle not too great for 

 that of their original deposition, while, on an east and west line, the slope 

 of these beds toward the centre of the basin is too slight to be susceptible 

 of angular measurement. As seen from the summit of Pilot Butte, whence 

 an extensive view is obtained over the basin country to the west and north, 

 the median line of greatest depression in these beds seems to extend in a 

 direction a little east of north from about the junction of Ham's Fork, cross- 

 ing the Green River, and extending up the valley of the Big Sandy, where 

 its outlines are marked by the prevailing white color of the bluffs formed 

 by the underlying beds of the G-reen River group. The outcrops of the 

 latter formation find their greatest development along the eastern rim 

 of the basin, while, on the west, they are comparatively thin and incon- 

 spicuous, especially toward the base of the Uinta Range', where they were 

 probably cut off by a shallowing of the Tertiary sea, or deposited uncon- 

 formably along the shore-line of slightly-raised beds of the Vermillion 

 Creek series. That to the north the sea of this epoch extended much far- 

 ther to the westward than the line of our exploration, is rendered probable 

 by the reported discovery of beds, having a close lithological correspondence 

 with those of this group, along Fontanelle Creek, a western tributary of 

 the Green River, and in the valley of Bear River, beyond our northern 

 boundary. 



The outcrop of the beds of the Vermillion Creek series, on the other 

 hand, which, throughout the region west of Green River, shown on this 

 map, are, in general, deeply buried beneath these later formations, find their 

 greatest development on the western rim of the basin, where they extend, 

 as will be seen on Map III, high up on the flanks of the Wahsatch Range, 

 increasing in thickness and in coarseness of material. Along the western 

 flanks of the Bitter Creek Ridges, the beds of this formation are exposed by 

 the denudation of north and south tributaries of Bitter Creek, but, in general, 

 are much disintegrated, and show few good outcrops. They are, however, 

 distinctly non-conformable with the beds of the Laramie group, but no dis- 

 tinct unconformity of angle was observed in these valleys between their 

 beds, and those of the overlying Green River series. They are also exposed 

 in the bottom of the upper portion of the valley of Sage Creek, and, as we 



