THEOIMES OF ORE GENESIS. 443 



and the tlieory of injection, so far as ores are concerned, is limited to some 

 very subordinate phenomena. Those remaining are variously subdivided 

 as occasion may require. With appropriate modifications there is every 

 reason to suppose that they include all important probable cases. It does 

 not follow that they present the subject in the most advantageous manner. 

 The least satisfactory form of the ascension theory asserts that the origin 

 of the ores lies below the deposits in some unknown position from Avhich 

 translocation has been effected by unknown means. Lack of facilities for 

 investigation may in some cases justify no more definite conclusion. In 

 other instances the nature of the occurrence may point to the conclusion 

 that the ores, though of unknown origin, have been deposited from solution 

 or by distillation. The ascension theory also includes cases in which there 

 is evidence, more or less satisfactory, as to the source whence the ore was 

 derived. This may be the interior of the earth, as is maintained by many 

 geologists, for some veins found in close connection with active volcanic 

 phenomena, or the origin may be sought in deep-seated rocks, stratified or 

 massive, but similar to those which are found at the surface. In either 

 case there may or may not be sufficient evidence to justify conclusions as 

 to whether the ores during their ascent were gaseous or in solution. 



The lateral secretion theory, as usually defined, is that ores are segre- 

 gated from rocks contiguous with the deposit. The statement that the lat- 

 eral secretion theory is applicable to a certain case does not convey any 

 implication as to the particular side from which the ore is derived. All ore 

 deposits are finite and any finite space may be filled from any one of six 

 directions. Neither does the lateral secretion theory, as such, involve any 

 conclusion as to the temperature of the solutions from which the ore has 

 been deposited. It is even possible that certain valuable minerals have 

 been laterally secreted by means of distillation, though this is no doubt an 

 exceptional and limited possibility. 



The modifications ot these two theories are best grasped in a tabular 

 form. 



