54 GEOLOGICAL HISTORY OF LAKE LAHONTAN. 



In all, there are at present between fifty and sixty groups of hot springs 

 in the Lahontan basin ; the total number of individual outflows cannot be 

 estimated at less than two or three hundred. It is impossible to estimate 

 the amount of water entering the basin from subterranean sources with 

 even an approximation to accuracy, but if gathered in a single stream it 

 would form a river comparable in size with the Humboldt during the sum- 

 mer season, the volume of which would remain practically constant from 

 year to year. The temperature of this imaginary river Avould be far above 

 the normal for the region ; and in composition it would be much richer in 

 dissolved minerals than ordinary surface streams, as is indicated by the 

 accompanying analyses. 



It is certain that many of the hot springs now flowing were in exist- 

 ence during the time that Lake Lahontan flooded the valleys of northwest- 

 ern Nevada; and it is believed that the three analyses given above not only 

 represent approximately the average composition of the springs now flowing, 

 but also indicate the character of the thermal waters that entered the ancient 

 lake through fissures in its bottom. 



EXTINCT SPRINGS. 



At many points in the Lahontan basin, as mentioned in the preceding 

 pages, we find deposits made by springs which are now extinct. The majority 

 of these are composed of calcareous tufa that was precipitated about sub- 

 lacustral springs, and will be described in the chapter devoted to the chem- 

 ical history of the former lake. A group of spring-mounds about half a 

 mile southward of Humboldt House and on the west side of the Central 

 Pacific Railroad track, are, however, of a diff'erent nature. They are low 

 domes composed principally of calcai'eous tufa, open at the top and filled 

 within with crystallized gypsum impregnated with sulphur. The presence 

 of sulphur has led to some exploration, but the supply is evidently too lim- 

 ited to be of much economic importance."^ The mounds in this group are 

 broad and comparativel} low domes, formed of thatch-like layers of calca- 

 reous tufa with considerable quantities of siliceous sinter, especially about 



23 These sulphur deposits were the only ones that could be found by the writer in the neighborhood 

 of Hunil)ol(U House, and are thought to be the ones described in the reports of the United States 

 Geological Exploration of the Fortieth Parallel, Vol. II, p. 74'2. 



