NO. 3 SMITHSONIAN EXPLORATIONS, IQI5 13 
Fic. 18.—One of the Three Sisters Springs filled with boiling hot water, 
through which bubbles of steam are rising. Photograph by Walcott. 
Fic. 19.—Great Sulfosel Hot Spring, about one mile northeast of Great 
Fountain Geyser, elevation 7,300 feet. The main opening of the spring has a 
temperature of 201.2° F. (93° to 94° C.). Water cools toward run-off in 
foreground, to 172.4° F. (78° C.). Siliceous deposits about this spring extend 
as cornices out over edges. Algal growth abundant in water at 134.6° F. (57° 
C.). Fine specimens were collected for National Museum. Photograph by 
Walcott. 
