PEALE.] PHYSICAL FEATURES OF DEPOSITS CHEMISTRY. 405 



small scale, the process by whicli the large cavernous pools were exca- 

 vated. He says : 



It would appear that in many cases, at least, tlio hot alkaline (?) water, as it 

 reaches the surface, is not thoroughly saturated with silica, and accordingly dissolves 

 away the walls of its orilices so as to undermine the surrounding area, the surface of 

 which falls in, until, in many cases, large caverns are excavated.* 



It seems to me probable that the opening of the vents Is generally 

 due to a violent breaking out of a mass of steam and water, and that 

 the size and character of the opening thus formed will depend upon 

 the character of the rock and soil through which it forces its way. That 

 geyser vents may be thus violently formed is proved by the steamboat 

 vent of the Gibbon Geyser Basin which broke out in 1878. The Cliii' 

 Caldron or Excelsior Geyser in the Egeria Group of the lower Fire Hole 

 Basin, in all probability, owes its origin to a similar violent outburst, as 

 its basin is bordered on three sides by rough, irregular walls of lam- 

 inated geyserite, which were evidently broken through by some force 

 acting at right angles to the plane of their deposition. 



The subject of the formation of the cones and craters of geysers is one 

 of exceeding interest, and will require a great deal of study of the 

 various forms. No place could be a better field for such study than is 

 the Yellowstone National Park. We are well aware that we have done 

 no more here than to indicate a few of the many thoughts suggested by 

 a casual glance at the field indicated. 



CHAPTEE IX. 



CHEMISTRY OF DEPOSITS. 

 By A. C. Peaxe, M. D., and Hjenry Leffmann, M. D. 



The deposits from the thermal waters may be generally classed under 

 three heads for the purposes of description here, viz: Travertine, Sili- 

 ceous sinter, and Aluminous or Mud Deposits. 



The first of these appears to be most widely distributed, and also oc- 

 curs most frequently as an ancient deposit. In this chapter we will 

 consider only the deposits of the Yellowstone National Park, except in 

 the tables where a few analyses of calcareous tufas or travertines from 

 other localities are inserted for the purposes of comparison. 



TRAVERTINE. 



Travertine, calc sinter, or calcareous tufa is always a deposit from 

 springs or rivers, and, according to Dana (System of IVliueralogy, p. 680), 

 the name travertine is a corruption of tiburtine from the Lapis Tiburtinus 

 of Vitruvius and Pliny. 



The two principal localities of travertine in the Yellowstone National 

 Park are the Mammoth Hot Springs of Gardiner's River and the Soda 

 Butte of the East Fork of the Yellowstone liiver. Only one analysis 

 was made from the specimens collected in 1878, and this is included in 

 the following table, being the second one mentioned : 



* Report United States Geological Survey of the Territories, p. 235. 



