1869.] The Alkaline Lakes of California. 15 



The most remarkable accumulations of alkaline waters are, however, 

 those of Mono Lake and Owen's Lake ; and of these, together with 

 the celebrated Boras Lake, I propose giving a short description. 



Mono Lake. — Mono Lake is about fourteen miles long from 

 east to west, and, in its broadest portion, nine miles wide from north 

 to south ; it was, however, formerly much larger than it now is, its 

 ancient shore-lines being very conspicuously indicated by a succession 

 of parallel terraces. 



On its south-eastern side a ravine has been eroded through the 

 sandy desert which surrounds it, to a depth of from sixty to a hundred 

 feet ; and in this cafion five well-defined terraces may be distinctly 

 seen. The level of the lake was once certainly at least 600 feet 

 higher than it now is ; and it is not improbable that it then com- 

 municated with the valleys both of the Carson and Humboldt, thus 

 forming a most important feature in the ancient geography of the 

 country. 



The waters of this lake, which have a high specific gravity, are 

 intensely alkaline and saline, removing grease readily, and being 

 far more detergent in their properties than ordinary soap-suds. 



They contain, in addition to common salt, large quantities of 

 carbonate and sulphate of soda, and apparently also a certain pro- 

 portion of lime, since large quantities of calcareous tufa have been 

 deposited along the lake-shore, and on the terraces far above the 

 present level of its waters. Near its northern shore are numerous 

 springs holding much lime in solution ; these have caused the form- 

 ation of extensive deposits of tufa, some of which rise above the 

 surface of the lake, resembling gigantic fungi of from six to ten feet 

 in height. 



In Mono Lake there are several islands, two of which are of 

 considerable size, — the larger being two-and-half miles in length, 

 whilst the smaller is about half-a-mile long. To the north of this 

 lies a group of volcanic islets of inconsiderable dimensions. On the 

 south-eastern corner of the larger island are numerous hot springs 

 accompanied by jets of steam, covering some thirty acres of land, 

 and extending into the lake itself, thus perceptibly raising its tempe- 

 rature for a considerable distance. 



The steam and heated gases thus escaping at the same time 

 fi-om hundreds of fumeroles, are often attended with considerable 

 noise, and deposit around the orifices of many of the apertures a 

 red incrustation, probably of chloride of iron : there is, however, no 

 smell of sulphur, nor any deposit of that substance. On the north 

 side of the island are two well-defined craters in the midst of hard 

 basaltic rock, but both are now filled with water. 



The smaller island is entirely composed of hard, dark basalt ; 

 and has at its western extremity a somewhat elevated volcanic cone 

 of black basalt capped by cinders. 



