NOTES ON I.AKK TAHOK, ITS TROUT AND TROUT-FISHING, 



139 



than u.'siial in Juiil", I'.lo-t, and was the liigliost .since 18(51. Powell records a fiuetiia- 

 tion of 5.5 feet (1.S91, p. 171). 



Origin of the l<ih\ — In discussintr the origin of Lake Tahoe, Le Conte states that 

 it is highly improbable that the basin was scooped out by glacial agencies; that, 

 rather, the lake was once wholly occupied by ice, a huge nier de glace. He is 

 inclined to the belief (1884, p. 45) that— 



* * * the small lakes near the southern and southwestern margin of Lake Tahoe are really 

 glacier-scooped rock Vjasins, yet the position of the principal lake, countersunk between two ridges of 

 the Sierra Nevada, seems to render it probable that its basin may, in reality, be a "plication-hollow" 

 or a trough produced by the formation of two parallel mountain ridges and afterwards modified by 

 glacial agency — that it is, in fact, a feature of mountain formation and not of glacial sculpture. 



Teiitperafuri'. — No attempt was made to obtain the temperature of the water at 

 any considerable depth; that is, beyond a depth of 425 feet. The following table 

 shows the results obtained by I^e Conte (1883, p. 509) and those ol)tiiined in this 

 investigation: 



The letter B indicates bottom temperatures. Le Conte states that he obtained the 

 .same general results in all parts of the lake and that his table is an abstract of his 

 average results. It will be noted that he obtained higher temperatures than those 

 obtained by me. This may be accounted for chiefly Ijy the fact that his observations 

 were made between the 11th and 18th of August, or a))out the time the water had 

 reached its maximum temperature for the summer, while mine were made on June 

 27, or before the water of the lake had been e.xposed very long to the warming 

 influence of the summer's sun. The temperature of the water in three of the creeks 

 was as follows: Blackwood Creek, 50° F.; McKinney Creek, 46.5-; Taylor Creek, 

 55.75°. 



There are some tiiermal springs at the northern end of the lake, one of which, at 

 Brockway, had a temperature of 130'^ F. The temperature of this water as it came 

 from the ground was probably somewhat higher, for this residing was made in a large 

 basin al)out 5 feet in diameter and several feet deep, and the warm water entered 

 the bottom of the basin. This thermal spring is oneof the attractive features of the 

 resort, as its water is palatable and is also utilized for bathing purposes. Le Conte 

 records a temperature of 131" F. for some of these thermal springs. 



The temperature of the air probably remains several degrees below the freezing- 

 point for a considerable period of time each winter, yet ice never forms on the lake 

 except in shallow, detached bays. "The true explanation of the phenomenon may, 



