FISH LAKE. 



263 



been unable to discover sufficient evidence to sustain ether view. Although 

 the traces of ancient glaciers are conspicuous in the vicinity, nothing can 

 be more sharply defined than the places where they terminated ; and we 

 are able to affirm confidently, by a comparison of places in close juxta- 

 position, that in one place the sculpture is due to glaciation and in another 

 it is not. It does not appear anywhere in this part of the plateaus that the 

 glaciers ever extended much below the 9,000 feet level, for at about that 

 level the terminal moraines cease and give place to other forms of sculpture. 

 As regards the possibility of a sunken block between two faults, it seems to 

 me that the evidence is not sufficient to establish it, and there is decided 

 evidence that it is an ancient valley of erosion, having its main features 

 marked out and partially developed before the present elevation of the 

 country had been reached. At the southwestern extremity is a low divide, 

 scarcely 30 feet above the water level, which forms the local watershed 

 between the Colorado drainage system and that of the Great Basin. At 

 present the lake drains into the Colorado system ; but at no distant epoch 

 it apparently drained into the basin system, flowing over this low divide. 

 Its ancient channel, leading down into Grass Valley (tributary to the Sevier 

 River), is as distinct and unmistakable as if it had dried up only a few years 

 ago. Mr. Howell, who recognized this channel and its obvious meaning, 

 supposed that the barrier now forming the divide had been produced by 

 morainal debris brought down from the Fish Lake Plateau and deposited 

 athwart the channel. More careful scrutiny, however, shows that the bar- 

 rier consists of volcanic rock in place. Hence it appears that the course of 

 the drainage has been reversed. Originally it flowed out of the lake to 

 the southwest ; but as the gradual uplifting went on the whole lake basin 

 was tilted, so that it began to flow out of the opposite end and over a low 

 barrier to the east and southeast. A very slight tilting only was required to 

 effect the change ; and a drop of 40 or 50 feet on the western side would 

 again reverse it to its original channel and pour it down the Awapa wall 

 into Grass Valley. 



A journey along the bank of the lake towards its outlet is instructive 

 as well as entertaining. The trail (I believe there is now a wagon-road) 

 leads along the base of the plateau wall, rising more than 2,000 feet above 



