396 



REPORT UNITED STATES GEOLOGICAL SURVEY. 



found only in regions of volcanic rocks, and to them we turn. Chemi- 

 cal analysis shows all lavas contain silica in the proportion of one-half 

 to four-fifths of their whole mass. Acid lavas contain 66 to 80 per 

 cent, of silica. Basic lavas contain 45 to 55 per cent, of silica. When 

 we examine the rocks of individual lo(?alities we find the same thing. 

 The following table gives some of them : 



Locality. 



Character of rocks. 



Percentage 

 of silica. 



Iceland 





72 3 



Iceland 





4L 28 







70 







70 to 81 







77 * 









*I'rom an analysis by Dr. Leffmann, 



But few of the rocks of the Park have been subjected to chemical 

 analysis, but the microscope shows that they belong to the vitreous 

 eruptive rocks. 



Bunsen was of the opinion that the silica of these rocks could be dis- 

 solved only by alkaline waters. He digested some of the Iceland rocks 

 in hot rain-water and obtained specimens identical with the water from 

 the geyser.* Mr. Eugene Robert found the basin of an old spring near 

 the Great Geyser in Iceland in which some of the rock had been altered 

 to a substance resembling kaolin. Chancourtois analyzed both this 

 and the unaltered rock. The latter contained 72.3 i^er cent, of silica 

 and the former only 65.8 per cent. Robert therefore inferred that the 

 silica in the water of the hot springs in Iceland was derived from the 

 phonolite, basanite, &c. (See Bischof's Chemical Geology, vol. ii, p. 

 455.) 



In the case of the deposits at Ischia and near Naples, Daubeny says 

 the alkali supposed to be efficacious in dissolving the silica in the Ice- 

 laud geysers, does not exist. In the Yellowstone National Park most 

 of the springs whose waters were analyzed were alkaline, but one of 

 them (Echinus Geyser, on Gibbon Geyser Basin) was decidedly acid, 

 and yet it contained over 19 grains of silica to the gallon. When water 

 is carbonated its solvent power is usually increased, but according to 

 C. Struckman t silica dissolves more readily in pure water than in car- 

 bonated water. It must be rem emberedthat in the depths where the 

 silica is dissolved by the water not only is there an enormous pressure 

 but an intense heat. We can but faintly imagine the effects of the 

 action of water upon the rocks at such high temperature and under such 

 enormous i3ressure. Steam doubtless has a powerful agency in the 

 work. Bischof found that the stones by which the Kaiserquelle at Aix 

 la Chapelle is closed, and the canals of the Schwerdtbad, at Burtscheid 

 (which consist of black marble), were converted into a doughy mass, 

 on the inner side, by the continued action of the steam, which had a 

 temperature of only 133° to 167^ F.| 



This agrees with what we observed at the Gibbon Geyser Basin in the 

 Park. At Spring No. 66 (see map of the Gibbon Basin, in Part I) is a 



* M, Strave took a quantity of clink stone from near a spring at Bilin, in Bohemia, 

 and after pulverizing it subjected it to the action of carbonated water, under a press- 

 ure of two atmospheres. Upon analysis it was found to agree closely in its comj)osi- 

 tion with the water of the spring. 



tAnu. Ch. u. Pharm. xciv, 337. 



t Researches on the Internal Heat of the Globe, p. 217. 



