W. H. Weed — Formation of Siliceous Sinter. 353 



carries 0*7620 gms. of silica to the kilogram of water, and 

 issues with a temperature of 199° F., one degree above the 

 theoretical boiling point of pure water at this altitude. This 

 water is perfectly clear and without sediment, and remains so 

 upon cooling to 35° F. and after standing several days. Yet 

 about the spring, sinter is deposited under such conditions that 

 evaporation can have but little effect, though it is also deposited 

 elsewhere through evaporation. It is possible that in this water 

 as in that of the Coral Spring, the influence of the silica already 

 deposited causes a separation from water that would not other- 

 wise deposit silica. 



Sinter deposition beneath the surface of the water is ex- 

 tremely rare among the hot springs of the Park and has never 

 been observed at either the Upper or Lower Geyser Basins. 

 The waters of the Coral Spring, JSTorris Basin, containing 0*6070 

 grams of silica to the kilogram of water, is opalescent from 

 silica in suspension or " pseudo solution," but does not de- 

 posit silica after standing several years in the laboratory, and 

 as in other siliceous waters cooling does not affect the silica, 

 which only separates out after freezing (crystallization). Yet 

 the water deposits silica freely upon the sides and bottom of 

 the spring. The constitution of this water, its peculiar opa- 

 lescence and the situation of the spring lead to the belief that 

 the saturation of the solution is due to chemical reaction be- 

 tween an alkaline spring water and acid vapor. This accords 

 with the theory of Damour regarding the deposition of silica 

 by the waters of the Iceland hot springs.* Moreover, in 

 such waters there is often a neutralization of the alkaline 

 solution by descending acid waters, made acid by oxidation ; 

 this is the way in which LeConte and Rising explain the de- 

 position of the gelatinous silica of Sulphur Bank, Cal.f 



That the carbon dioxide of the atmosphere has any effect 

 in producing sinter deposition *{: is disproven by the occurrence 

 of free C0 2 in these waters. 



Evaporation, partial or complete, certainly produces a depo- 

 sition of silica from the siliceous waters of the Park, both acid 

 and alkaline. It is, according to Bunsen, the only cause pro- 

 ducing the deposition of sinter by the geyser waters of Ice- 

 land. Though evaporation is certainly an efficient agent, par- 

 ticularly in the dry air of the Park, producing some of the most 

 beautiful and striking forms of sinter known, yet the deposits 

 of the Yellowstone (excepting those of Norris Basin) are but 

 partly due to this cause, and as already stated, are chiefly formed 

 by a separation of silica by the vegetable life of the hot water. 



*Phil. Mag., xxx, 1847, p. 405. 



f This Journal. Ill, vol. xxiv, p. 33. 



JRoseoe and Schorlemmer, Treatise on Chem., vol. i, p 571. 



