244 QUICKSILVER DEPOSITS OF THE TACIFIC SLOPE. 



scarcely intelligible except upon the supposition that its principal features 

 are due in great measure to those of the original lava surface ; for it 

 presents a series of elongated basins either without apparent outlets or with 

 only very narrow, sharply cut outlets, and these depressions either contain 

 permanent lakes, like Thurston, or winter pools, like some others in the 

 neighborhood, or present flat surfoces of fine soil, evidently the result of the 

 silting up of lakes. These areas of sedimentation, flanked as they are bv 

 massive ridges of lava, cannot be due to erosive agencies, and there is 

 nothing whatever to indicate that they are due to ox'ographical changes 

 postdating the andesite eruptions. 



Thurston Lake. — Tliurstou Lake is a peculiar body of water, suri-ounded on 

 three sides by heavv masses of andesite, with high and steep slopes. On 

 the fourth side, toward the northwest, the lake bottom rises at a verv slight 

 angle and merges i«to an elongated valley of considerable length. The 

 addition of a few feet of water would double the length of the lake in this 

 direction, while adding almost imperceptibly to its e.xtent elsewhere. The 

 water marks show that the height of water varies about eleven or twelve feet. 

 In spite of its lack of any visible outlet, this lake is fresh and abounds 

 in animal life, some of the fish being apparently of the same species as 

 those of Clear Lake. Its fluctuation is also sensibly the same as that of 

 Clear Lake, and, as nearly as can be estimated wdthout a special survey (a 

 task which the dense brush would render very expensive), its level is the 

 same. The onlv probable explanation of these facts would seem to be that 

 there is an underground passage between the lakes — a supposition in which 

 there is no inherent improbability, since channels such as that supposed 

 frequently exist in volcanic masses, especially within a moderate distance 

 of their original surfaces. 



Little Borax Lake. — As lias bccu sceu, there is much structural evidence to 

 show that the andesitic rock of Konocti Mountain is not recent, but that it 

 is geologically of late origin. The surroundings of Little Borax Lake, how- 

 ever, seem to indicate a local activity long postdating the andesitic erup 

 tion. This little saline body of water lies in a crater-like depression at the 

 foot of the mountain, a portion of the walls being very abrupt and evidently 

 representing fractured surfaces, while the basin itself contains very little 



