292 E. C. ANDBEWS. 



Part III. 



Applications of the Ice Flood Hypothesis. 



1. The Californian Sierras.— We may consider two 

 classes of valleys common to these ranges, namely, any of 

 the higher valleys such as Bloody Oanon, Rock Creek or 

 the upper San Joaquin tributaries, as illustrating one class, 

 and any of the Yosemite valley types for the other. The 

 following observations were made in company with Dr. 

 G. K. Gilbert and Mr. Willard D. Johnson during the late 

 summer of 1908. The following notes will not clash with 

 the work of these geologists in California. Brief reference 

 here is made only of such facts as are pertinent to the dis- 

 cussion of the "Ice Flood Hypothesis." 



Preliminary. — The higher Sierran summits apparently 

 represent remnants of an old surface. Beneath this a 

 " valley in valley" appearance is found, the upper valley 

 floors being wide while the younger and lower valleys are 

 of the "profound canon" type. 



(a) Rock Creek Canon and San Joaquin Basin. — Several 

 facts stand out prominently upon even a casual study of 

 these valleys. The valleys are steep-sided, often of great 

 depth, and they are characterised by an absence of over- 

 lapping spurs. Blunt or truncated spurs at times present 

 huge facets to the valleys. The floors, when considered 

 generally, are flat and broad, but show minute irregularities 

 of detail, frequently presenting a partially moutonneed and 

 a partially quarried appearance. The floor is frequently 

 interrupted by huge "steps" with intervening "treads" on 

 heavy declivities, and these possess modified cirque forms 

 at their heads. Each "interstep tread" may possess one 

 lake or a series of lakes or rock basins dotting its surface. 

 These rock basins most frequently characterise the upper 

 parts of the valley floors, while lower down stream, where 

 the much heavier water volume occurs, the lake basins are 



