570 GEOLOGY AND MIIn^ING INDUSTEY OF LEAUVILLE. 



legitimate inheritors of the ascension or injection theory, now modified into 

 the sublimation theory, themselves admit that it is practically an aqueous 

 solution, even if in a gaseous form, from which they derive the metallic con- 

 tents of their deposits.^ And among those Avho professedly maintain that 

 most ores are probably deposited by percolating waters, but who would dis- 

 tinguish lateral secretion from ascension or descension, there is fundament- 

 ally so much held in common that dift'erences seem slight." 



That some ore deposits have necessarily been deposited from solution 

 is admitted by all geologists who have made special studies of the subject, 

 and that the greater xjart of them have been so formed is maintained b)- a 

 large and ever-increasing class. Geological investigations have also shown 

 that within the rocks forming the crust of the earth, so far as observation 

 has yet reached, there is a constant circulation of waters carrying more or 

 less mineral matter in solution, and that no rock is absolutely impermeable. 

 There are therefore both upward and downward currents, it being gener- 

 ally assumed that the latter are surface waters sinking under the influence 

 of gravity and the former the same waters rising under that of the internal 

 heat of the earth. It will be readily apparent, however, that such move- 

 ment is not necessarily vertical in either direction, but will take its immedi- 

 ate direction from the character of the rock mass through which it is passing; 

 that there will be a tendency of waters, filling capillary passages and minute 

 fissures, to seek larger channels on joint, fault, and stratification planes, 

 along which their movement will be more free; further, that, in case of 

 waters passing along such channels and carrying mineral matter in solution, 

 this mineral matter will be deposited where the conditions of the inclosing 

 rock are such as to favor a chemical precipitation or interchange, and that 

 such precipitation will be most abundant where for any cause there is some 



A. (le Lappaieat, TraiW de Geologic, p. 1170. Paris, 1883. 

 '^Thu9 Joseph Le Conte, in his article on the Genesis of Ore Deposits (Amer. Jour, of Sci., May, 

 1883), while devoting much space to disproving the theory of Sandberger, as exposed in his recent 

 Researches on Ore Deposits, is really of the same opinion us the latter on most essential points. The 

 main point of difference between the two appears to be that, while Le Conte maintains that the phe- 

 nomena of Steamboat Springs and Sulphur Bank, where deposits are actually going on at the jiivsent 

 d.iy, should be taken as a type of all deposits aud may serve as a basis for a general theory. Sand- 

 berger considers them exceptional cases aud their conditions not necessarily the same that |)revailed 

 with deposits formed at a great depth belmv the surface. 



