440 QUICKSILVER DEPOSITS OF THE rACIFIC SLOPE. 



pothesis it is certainly difficult to conceive that all the sulphur compounds 

 should be confined to the surface of the earth or that all the sulphur com- 

 pounds not occurring' near the surftxce should be oxidized. 



liorax is another component of the spring- waters which it is difficult 

 to account for, except on the hypothesis that the waters derive a portion 

 of their mineral constituents from beneath the g-ranite. Ordinary surface 

 waters seldom, if ever, contain more than a mere trace of borax, so that it 

 is highly improbable that currents descending toward the source of heat 

 carry a large [)ercentage of borax with them. The only boron mineral 

 which is anywhere abundant in granite is tourmaline, but this mineral is so 

 rare in the granites described in this memoir that not a single grain of it has 

 been detected in the slides. It is somewhat improbable, therefore, that the 

 waters ascending through the granite have derived the large quantities of 

 borax which they contain from that rock. This improbability is strength- 

 ened by the well known fact that boric acid accompanies the direct sul- 

 phurous emanations of many volcanic vents It is indeed conceivable that 

 the borax should be derived from sedimentary rocks, but on the one hand 

 there is no reason to suppose that the granite of Steamboat Springs overlies 

 any sediments and on the other hand it seems doubtful whether strata ever 

 contain any considerable quantity of borax except where they have derived 

 it from volcanic emanations in the neighborhood. It is usual, and appears 

 rational, therefore, to ascribe the borax of hot springs to a volcanic source 

 the character of which is luiknown. The waters of Steamboat Springs and 

 Sulphur Bavd<, it will be remembered, contain relatively large quantities of 

 borax, which is also present in the Knoxville mineral springs. 



Depths at which solvents are found. — Whether tlic liydrogcu sulpliido of those 

 thermal springs which are associated with other volcanic phenomena is due 

 to tlie reduction of soluble sulphates by organic matter by some unknown 

 process not involving the production of hydrocarbons, or whether it is due 

 to purely inorganic reactions not yet elucidated, as seems to me more prob- 

 able, it is evident tint this gas raaches the surface fro'.n c:).i-5iderable depths, 

 at which the waters percolating from the surface meet with rocks of greatly 

 elevated temperature. In cases like those of Steamboat Springs and Sul- 



