INCOKGKUTTIES OF PREVAILING HYPOTHESIS 357 



work is visible. Catchment basins there are large. After all his discus- 

 sion, Gilbert himself is compelled to admit that 



"If the rainfall in Bonneville times was very great, as compared with the 

 modern, these catchment districts should have furnished tributary streams; 

 and such streams flowing over tracts of alluvium, the accumulation of ages, 

 should have transported large quantities of it to the margin of the lake and 

 constructed deltas of it. We seem thus to have an intimation that the climatic 

 change, whatever its nature, did not affect the rainfall in a degree commen- 

 surate with the difference in area of lake surface." '' 



NON-COINCIDENCE OF LAKE AND GLACIAL EPOCHS 



Since Gilbert's Bon]le^'ille studies were made, so many new facts about 

 the region have been recorded that no longer does appeal have to be con- 

 fined to a period of giaciation in order to find an adequate explanation 

 for the gathering of waters of a great desert lake. In fact, in point of 

 time the formation of the lake and the advance of the continental ice- 

 sheet do not now appear to be exactly contemporaneous. The lake seems 

 to have been well along toAvard complete desiccation before the Glacial 

 epoch set in. Glacial causes may have affected the level of the lake in 

 some of its later stages, but certainly not in its earlier ones. The notion 

 of dependence of lake on glacial climate is obviously a forced conclusion. 



INFELICITOUS COMPARISON OF LAKES OUTLET WITH NIAGARA 



The attempt to establish an analogy between Lake Bonneville and Lake 

 Erie and between the Niagara Eiver and the Red Rock Pass outlet is, as 

 it now ajjpears, a fatal o1)Jcction to tiie prevailing hypothesis of origin of 

 the desert lake. Nowhere in the Red Rock Valley is there the slightest 

 trace of an old gorge, the formation of which is not so remote but that 

 there would have remained conspicuous walls several hundred feet high. 

 Gilbert regards the old hypothetical outlet as possibly larger than the 

 Niagara River and capable of draining the lake in 25 years.^ This rate 

 necessitates the assumption of an cxtensi\'c and hitherto unknown rapidity 

 of cutting back of the Red Rock Pass falls and an excavation of at least 

 400 feet in depth before the lake would cease to overflow its rim. 



Lajder these circumstances, it is strange that the lake apparently con- 

 tinued to lower its level with the same speed after the supposed outlet no 

 longer remained such as it did before. No doubt the Niagara coloring is 

 much too dee]) for desert conditions. 



•'' Mon. U. S. Gool. Siii-vey, vol. i, 1S<.)0. p. 1C,7. 

 « Mon. U. S, Geor Siu'veyj vol, i, 1890, p. 170. 



