646 RECORD OF MEETINGS OF THE 



the production of sulphuric acid from the natural metallic 

 sulphides, is actively in progress. Carbonic acid enters also 

 with the meteoric waters. The rocks are open in texture 

 and favorably situated for maximum change. From this zone 

 we can well imagine that all the finely divided metallic par- 

 ticles which are widely and sparsely distributed in the rocks 

 go into solution and tend to migrate downward into the quiet 

 and relatively motionless ground-water. If the acid solutions 

 escape the precipitating action of some alkaline reagent such 

 as limestone they may even reach the ground-waters, and 

 their dissolved burdens may be contributed to this reservoir, 

 but the greater portion seems to be deposited at the level 

 of the ground-water itself or at moderate distances below it. 

 Impressed by these phenomena, which present a true cause of 

 solution, and influenced by their familiar and everyday char- 

 acter, we may build up on the basis of them a general concep- 

 tion of the source of the metallic minerals dissolved in those 

 aqueous solutions which are recognized by all to be the agents 

 for the filling of the veins. 



Let us now focus attention on the ground-water. This 

 saturates the rocks, fills the crevices, and forces the miner who 

 sinks his shaft to pump, much against his natural inclination. 

 The vast majority of mines are of no great depth, and the 

 natural conclusion of our earlier observers, based on this expe- 

 rience, has been that the ground-waters extend downward, 

 saturating the strata of the earth to the limit of possible cavi- 

 ties, distances which vary from 1,000 to more than 30,000 

 feet. To this must be added another familiar phenomenon. 

 The interior temperature of the earth increases at a fairly 

 definite ratio of about one degree Fahrenheit for each 60-100 

 feet of descent. In round numbers, if we start with a place 

 of the climatic conditions of New York — that is, with a mean 

 annual temperature of about 51 , we should on descending 

 10,000 feet below the surface find a temperature of about 212 , 

 and if we go still deeper it would be still greater. Of course, 

 under the burden of the overlying column of water, the actual 

 boiling points for the several depths would be greater, and 

 it is a question whether the increase of temperature would 



