444 QUICKSILVER DEPOSITS OF THE PACIFIC SLOPE. 



Ore deposits are formed — 

 By ascension — 



(1) From unknown sources; 



(a) By unknown methods; 



(h) By deposition from hot solutions; 



(c) By distillation, with or without steam. 



(2) From known sources: 



(a) From the original interior of the earth: («), (h), 



and (c), as above; 

 (/?) From underlying rocks: (a), (h), and (c), as above. 

 By lateral secretion (from contiguous rocks on any side) — 



(1) Due to heated waters rising from below, charged with 



reagents ; 



(2) Due to cold surface waters, which become charged with 



reagents in permeating the rocks; 



(3) Due to distillation (a rare and unimportant case). 



It will be observed that the difference between the lateral secretion 

 theory and the ascension theory depends simply on contiguity, so that, as 

 von Cotta pointed out, the ascension theory, as applied to rocks contiguous 

 to an ore deposit, becomes a case of the lateral secretion theory. For the 

 present purposes of economic geology the nomenclature of the theories is 

 not well chosen. Many investigators are at present anxious to trace those 

 cases in which ores are derived from rocks accessible from the surface, and 

 the main question with mining geologists is now whether or not it is possi- 

 ble to prove the derivation of given ores from rocks existing in the neigh- 

 borhood of the deposit, and, if so, how the solution and deposition have 

 been effected. It is a matter of detail whether the ore deposit is actually in 

 contact with the rock from which it has been derived or is separated from 

 it by masses of rock which exert no sensible effect upon the solutions. 



It is very easy to regroup the special forms of the lateral secretion and 

 ascension theories with reference to this point, and tlie subject seems to gain 

 considerably in simplicity by this step, as shown in the following state- 

 ment. 



