UTAH LAKE VALLEY. 441 



spar. Of the sedimentary rocks which underlie this trachyte flow, only a 

 few exposures were found along the northern slopes of the eastern half of 

 the Traverse Mountains. They consist of white quartzites, and, in a cut 

 made by the railroad not far from the point of the hills, of a blue quartzite 

 having the external appearance of a limestone. Their structure-lines were 

 too much obscured to afford indications of their age on strati graphical 

 grounds, but, from their lithological habit, they have been provisionally 

 assigned to the Cambrian quartzites, which they most resemble. 



The trachyte of the western portion of the Traverse Mountains is a 

 reddish rock, containing large crystals of sanidin and considerable bronze- 

 coloi-ed mica, together with some hornblende. The groundmass is very 

 vesicular, and contains some glassy base. In Rose's Canon is found alight- 

 gray trachyte, having a laminated structure, rich in crystals of hornblende 

 and mica, showing comparatively few macroscopical crystals of sanidin. 

 While tlie dark trachytes of the range belong rather to the normal sanidin- 

 trachyte group, this rock may be more properly classed among the horn- 

 blende-trachytes, and somewhat resembles the andesite above mentioned, 

 which probably came from near the same locality. Near the mouth of 

 Bingham Canon was found a rock which, in the field, was considered a 

 rhyolite, consisting of a breccia-like felsitic groundmass, containing grains 

 of free quartz ;' but, as the specimens obtained have been lost, the occurrence 

 has not been colored upon the map. 



U TAH Lake Valley. — Utah Lake is a beautiful body of fresh water, 

 about 20 miles long by 4 or 5 miles in width, which receives the drainage of 

 the southern portionof the Wahsatch Mountains and a portion of that of the 

 southwest slopes of the Uinta Range. It is nearly 300 feet above Salt Lake, 

 into which its sur[)lus waters flow through the Jordan River. Like the 

 latter lake, its shores are very flat and shallow, especially along the eastern 

 side, where the valley-slope from the foot-hills of the Wahsatch Range to 

 the water's edge is even less than in the Salt Lake Valley. The old lake- 

 terraces form prominent lines along the faces of the mountains which sur- 

 round it, and are especially developed at the gap in the Traverse Mountains 

 through which the Jordan River flows, and where they show immense accu- 

 mulations of fine gravel. The upper terrace-line, which could be distinctly 



