68 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 54. 



not be determined certainly. One of them (Yankee Doodle Lake), 

 reputed locally to be "bottomless," I fomid to measure about 25 

 feet. The rugged inclines surrounding these lakes are covered with 

 large angular fragments of rock, and the bottoms of the lakes are 

 largely of the same material and usually practically devoid of silt 

 and entirely without vegetable mold. The water, derived from 

 melting snow on the slopes above, is very clear, and in many lakes, 

 when viewed from above, presents a brilliant green color. 



A striking feature of these lakes is the great amount of snow which 

 accumulates on the cirque walls above, in some of them extending 

 well out over the ice cover of the lake. A lake so covered is long in 

 becoming free from ice and the water remains at a low temperature all 

 summer, so that climatic differences between alpine lakes are deter- 

 mined by the size and position of such snowbanks rather than by 

 elevation.- 



At the beginning of June, even in warm seasons, all of these lakes 

 are completely covered with ice, and in 1912, a season of heavy snow- 

 fall and delayed spring, the breaking up of the ice did not begin until 

 early in July. In those where much snow extends over the ice the 

 process is greatly delayed, as an extreme of which we have Ice Lake 

 (12,188 feet), which on August 28, 1912, was still about half covered 

 with ice and had a temperature of 40° F. (See lower fig., pi, 14.) It 

 is probable that the ice did not entirely melt during the summer and 

 that the temperature did not rise above 45°. I have made no obser- 

 vations of the time of freezing of these lakes in the autumn and have 

 been unable to get definite information, but, judging by general 

 weather conditions in this region, the temperature of the water must 

 begin to decrease early in September and it is probable that by the 

 end of the month they are frozen over. By records made at times 

 of studying each lake it has been learned that, at the time of breaking 

 up of the ice, the surface temperature is 35° to 37° F. and by the 

 time the last floating pieces have melted it has reached about 44.° 

 It then rises rapidly to about 52°, where it remains without much 

 change as long as any considerable mass of snow persists on the cirque 

 walls above to furnish cold water. In all alpine lakes except the 

 few where there is insufficient snow to last well through the simimer 

 52° F. is about the maximimi temperature. 



The striking conditions then, which characterize the alph^e lakes 

 are short season (two to three months free from ice) and the low 

 temperature even during the warmest part of the year (a maximum 

 of about 52° F.). (See fig. S.) 



Though it is not in aU cases possible to assign a given lake definitely 

 to one group or the other, yet, for the most part, the alpine lakes 

 form a well-defined group, quite distinct from any of the kinds of 

 lakes which must be included in the montane group. 



