270 GEOLOGY OF THE HIGH PLATEAUS 



a broad valley parallel to the one just left. This has been named Moraine 

 Valley, from a rather large and conspicuous relic of glacial times, which 

 could not escape observation because it is so well preserved and tells its 

 story so plainly. It fills a lateral valley, heading near the summit of Mount 

 Ten-ill and extending eastward into the broader expanse of Moraine Valley. 

 It is covered with pools and lakelets bowered with aspen and spruce, and 

 has the ordinary terminal character where its proper bed opens into Mo- 

 raine Valley ; beyond which no traces of glaciation are recognizable. The 

 altitude of the termination is veiy nearly 9,000 feet, showing the same gen- 

 eral fact which has already been spoken of, that the glaciers did not, in 

 this part of the country descend to low levels, but were confined to the 

 highest parts of the region. 



In the northern part of Moraine Valley the sedimentary beds are occa- 

 sionally revealed in insulated exposures surrounded by trachytic and ande- 

 sitic beds in an advanced stage of decay. They are of Tertiary age and 

 are found on the western side of the valley, where considerable spaces are 

 uncovered. They dip slightly towards the east, being, in fact, the eastern 

 branch of an anticlinal swell, while the beds of Summit Valley form the 

 western branch and Mount Terrill occupies the summit. (See Sec. 3, 

 Atlas Sheet No. 6.) Their Tertiary age is inferred from their position, 

 but no fossils have been obtained from them. The volcanic rocks of the 

 northern part of the valley seem to have been of much greater volume 

 formerly than at present, and to have been much wasted by erosion, though 

 it is also inferred that they were never so extensive and massive here as to 

 the southward. They are all, so far as observed, trachytic ; some of them 

 belonging to the dark hornblendic division, others to the sanidin division, 

 the latter predominating upon the western side of the valley. 



The principal drainage is to the southward, running parallel for a con- 

 siderable distance to that from Summit Valley, and at length the two unite 

 and form a noble stream as large as the Sevier, which has volume enough 

 to reach the Colorado. The northern part of the valley is drained by a 

 few rills, which find their way into Gunnison Valley to the northeast and 

 thence through Salina Canon to the Sevier. Thus the divide between the 



