344 GEOLOGICAL EXCURSION TO THE KOOKY MOUNTAINS. 



of these calcareous deposits from the hot waters which have given the 

 aame to the mountain. Lying upoD the surface of this travertine on 

 the top of the mountain are found glacial boulders brought from the 



summit of the (Jallatin range, 15 miles away, which have been trans 

 ported on the ice .sheet across Swan valley and deposited on the top of 

 the mountain, TOO feet above the intervening valley. They offer the 

 strongest possible evidence that the travertine is older than the glacier 

 Which has Strewn the county with transported material. How much 

 travertine was eroded by ice it is, of course. Impossible to say, but so 

 friable a material would yield readily to glacial movement. 



The number of hot springs found in the Park exceeds 4,000. If to 

 these be added the fumaroles and fissures, from which issue in the 

 aggregate enormous volumes of steam and acid vapors, the number 

 of active vents would be more than doubled. There are about 100 

 geysers in the Park. Between a geyser and a hot spring no sharp 

 definition can be drawn, although a geyser maybe defined as a hot 

 spring throwing, with intermittent action, a column of water and 

 steam into the air. A hot spring may boil incessantly without violent 

 eruptive energy; a geyser may lie dormant for years without any 

 explosive action and again break forth with renewed force 



The thermal waters of the Park maybe classed under three heads: 

 first, calcareous waters carrying calcium carbonate in solution; second, 

 siliceous acid waters usually carrying free acid in solution; third, sili- 

 ceous alkaline waters rich in dissolved silica. 



Calcareous waters are confined almost exclusively to the Mammoth 

 Hot springs, where they have built up enormous deposits of travertine 

 with only traces of salts of magnesia and alkalies. The travertine con- 

 tains from 9.~> to 00 percent of calcium carbonate. The .Mammoth Hot 

 springs lie just north of the northern escarpment of the Park plateau, 

 and while they break out in close proximity to rhyolite bodies and 

 undoubtedly receive their heat from volcanic sources, they reach the 

 surface through Mesozoic strata, which here form the surface rocks. 

 Jurassic and Cretaceous limestones have furnished the lime held in 

 solution and precipitated as travertine. With a few insignificant excep- 

 tions, only siliceous waters are found issuing from fissures in the 

 rhyolite rocks, from which they derive their mineral contents. Acid 

 waters may usually be recognized by efflorescent deposits of alum and 

 soluble salts of iron, and frequently by the presence of delicate crystals 

 of sulphur. These acid waters possess an astringent taste. Although 

 jar less common than the alkaline waters, they occur scattered over 

 the plateau at a number Of localities and maybe found at the High- 

 land springs, on the west slopes of Mount Washburne, and in the 

 Xorris Basin. Alkaline springs present more of general interest than 

 the acid waters, as it is only in connection with the former that the 



