MOUNT MARVINE— MORAINE VALLEY. 269 



under the northeast corner of the Fish Lake Plateau. They are Lower 

 Eocene, equivalent to the Bitter Creek of Powell. 



The altitude of the ridge forming Mount Terrill declines towards the 

 south until a lofty col or "saddle" is reached, which divides it from Mount 

 Marvine. The latter is one of the most striking features of the region. It 

 is a long ridge reduced to a mere knife-edge at the summit, and having 

 rocky fronts on either side, sloping about G0°. A transverse section of 

 the upper 2,000 feet of the mountain would be an equilateral triangle. 

 For several years it was named by our parties The Blade. When seen 

 from the south or north it has a most abrupt and peaked appearance, which 

 becomes more pronounced the nearer we approach it. Viewed laterally 

 from Summit Valley at its base, it presents a serrated summit, notched with 

 many gaps and bristling with many cusps. The altitude of the mountain 

 above the valley is about 2,700 feet and 1 1,400 feet above the sea. It con- 

 sists of alternating trachytes and augitic rocks, resting upon Lower Eocene 

 strata. The thickness of the volcanic beds is, in the aggregate, from 1,200 

 to 1,800 feet, being least at the northern end, and increasing towards the 

 south. There is a succession of beds having the same general lithological 

 characters as those in Fish Lake Plateau, except that the augitic members 

 seem to be less numerous but more massive. Here, also, the dominant rock 

 is the argilloid variety of trachyte. 



The origin of this mountain becomes quite apparent when studied from 

 both sides. It has been isolated, like a gigantic butte, from the adjoining 

 country by the erosion of the valleys upon either flank. The inception of 

 this work is very ancient, since it undoubtedly antedates the uplifting of the 

 platform on which the mountain stands, and may therefore be referred to 

 any epoch more ancient than the latter part of the Pliocene and more 

 recent than the Eocene. 



MOUNT HILGARD AND MORAINE VALLET. 



Before proceeding southward it is desirable to look briefly at Mount 

 Hilgard and at the intervales which separate it from Mounts Temll and 

 Marvine. From Summit Valley we may easily cross the col which separates 

 the two latter summits, and descending the other side we find ourselves in 



