162 DESCRIPTIVE GEOLOGY. 



of varying thickness of dark-blue earthy limestone, from which was obtained 

 Pleurophorus oNongus and some fragments of a strongly-curved Produdus. 

 Above the blue limestone is a bed of 40 feet of dark, earthy limestone, 

 frequently of reddish color, followed by 40 feet of grayish granular lime- 

 stone. This thickness of 200 feet of limestones is overlaid by 50 feet of 

 arenaceous shales, beyond which is a gap of about 500 feet, showing only 

 occasional outcrops of thin arenaceous shales, but including probably 

 argillaceous and calcareous beds in the intervals covered by soil. A gap of 

 . some 400 feet now occurs before the ridges of the characteristic red sand- 

 stones of the Triassic are reached. Near the base of these, in a bed of light- 

 drab, fine-grained, semi-crystalline limestone, was found a Natica Leila. 

 Individuals of the same species were found in a similar position in a lime- 

 stone of the Red Beds on the East Fork of the Duchesne in the Uinta 

 Range. This species, being new, does not suffice to characterize the 

 horizon, but is interesting as being the only one found between the hori- 

 zons of distinctly Jurassic and Permo-Carboniferous types. 



The beds thus far noticed occupy the higher portion of the ridge, 

 whose surface is but little incidented. On this ridge there is evidence of 

 one, if not two, slight displacements along a line approximately at right 

 angles to the strike of the beds. From the fragments of granite seen along 

 the principal line, it would seem probable that a sharp ridge branches out 

 from the main granite body to the westward, which has determined the 

 direction and position of the faulting. Along the western slopes, the harder 

 or more massive beds of the Mesozoic formations stand out in monoclinal 

 ridges, and are easily distinguished by their lithological habit. These 

 upper beds where observed have a steeper dip than those nearer the axis 

 of the fold; their angle being over 40° to the westward, while that of lower 

 beds is scarcely 30°. In general direction of strike, they follow the shape 

 of the uplift, curving eastward toward the south, and toward the north 

 assuming a trend of due north and south ; the line of the ridges is, however, 

 rather sinuous and irregular, following short re-entering and projecting 

 angles, and consequently presenting varying dips. 



The Triassic formation is represented by a thickness of about 600 feet 

 of sandstones, of a light pinkish red and more massive habit in the uppei 



