764 . ABSTRACTS OF PAPERS 



The fuller history of the Glacial period is better studied east of Toronto, 

 where the strata are exposed in Scarboro Heights. 



ORIGIN OF CLIFF LAKE, MONTANA 

 BY G. R. MANSFIELD^ 



(Abstract) 



Cliff Lalie lies in south central Montana about 5 miles northwest of the 

 continental divide, where the latter makes the pronounced bend that partly 

 encloses the basin of Lake Henry in eastern Idaho. The lake was brought to 

 public notice in 1872 by Hay den, who described it as formed in a volcanic 

 fissure. At the present time popular belief ascribes the lake to a similar 

 origin. The paper discussed the evidence for the hypothesis of volcanic origin 

 and presented alternative evidence to show that the lake, though set deeply 

 in a lava plateau, really occupies a portion of a river valley that was inter- 

 rupted in early maturity by the advent of a glacier which left a series of 

 morainic dams and thereby produced a group of small lakes, of which ClifiE 

 Lake is perhaps the most notable. 



Discussion 



Prof. W. M. Davis suggested the possibility that landslides from the steep 

 valley sides might explain the formation of the lakes, and noted the fact that 

 the hummocky surfaces of landslides often simulate the form of moraines. 



Professor Mansfield replied that the possible effect of landslides had been 

 considered by him, but that the evidence appeared to favor a glacial origin 

 for the obstructions which held in the lakes. 



ROCK STREAMS OF VET A MOUNTAIN, COLORADO 

 BY H. B. PATTON 



Published as pages 663-676 of this volume. 



Discussion 



Prof. D. W. Johnson expressed his appreciation of the very instructive 

 lantern slides shown by Professor Patton, and recalled an example of rock- 

 streams in the so-called crater of the San Francisco Volcano, in Arizona, 

 which terminates in a high and steep crescentic slope, and which he at first 

 interpreted as a terminal moraine. 



Dr. F. E. Matthes : On the northeast side of Pikes Peak there occur several 

 deep, cirque-like depressions containing what appear to be strong morainic 

 ridges composed of rock debris. The glacial origin of the latter features 

 seemed, at the time of observation, beyond doubt. They may, however, turn 

 out to be rock-streams like those described by Professor Patton, and renewed 

 examination of them seems therefore desirable. 



Professor Patton said in reply that he had at times been inclined to at- 

 tribute somewhat similar structures in high mountains to creep of the rock 

 detritus, influenced by presence or absence of parallel snow-drifts, but that 



' Introduced by U. S. Qrant. 



