THE PROBLEM OF THE METALLIFEROUS VEINS. 199 



IMay we now draw all these facts and supposed or assumed 

 phenomena into one whole I 



The descending meteoric waters become charged with dissolved 

 earthy and metallic minerals in their downward, their deep-seated 

 lateral, and perhaj^s also at the beginning of their heated uprising 

 journey. They are urged on by the head of the longer and colder 

 descending column and by the interior heat. They gather together 

 from many smaller channels into larger issuing trunk channels. 

 They rise from regions of heat and pressure which favor solution, 

 into colder regions of precipitation and crystallization. They de- 

 posit in these upper zones their burden of dissolved metallic and 

 earthy minerals and yield thus the veins from which the miner draws 

 his ore. 



This conception is based on phenomena of which the greater part 

 are the results of everyday experience. It is attractive, reasonable, 

 and is on the whole the one which has been most trusted in the past. 

 Doubtless it has the widest circle of adherents today. It is, how- 

 ever, open to certain grave objections, which are gaining slow but 

 certain support. 



The conception of the extent of the ground water in depth, for 

 example, is flatly opposed to our experience in those hitherto few 

 but yearly increasing deep mines which go below 1,500 or 2,000 feet. 

 A\Tierever deep shafts are located in regions other than those of 

 expiring but not dead volcanic action, they have passe'd through the 

 ground M^ater, and if this is carefully impounded in the upper levels 

 of the mines and not allowed to follow the workings downward, it 

 is found that there is not only less and less water but that the deep 

 levels are often dry and dusty. Along this line of investigation, 

 Mr. John AV. Finch, recently the State geologist of Colorado, has 

 reached the conclusion, after wide experience with deep mines, that 

 the gromid waters are limited, in the usual experience, to about 

 1,000 feet from the surface and that only the upper layer of this is 

 in motion and available for springs. 



Artesian wells do extend in many cases to depths much greater 

 than this and bring supplies of water to the surface, but their very 

 existence implies waters impounded and in a state of rest. 



To this objection that the ground waters are shallow it has been 

 replied that when the veins were being formed the rocks were open- 

 textured and admitted of circulation, but subsequently the cavities 

 and waterways became plugged by the deposition of minerals by a 

 process technically called cementation, and the supply being cut off, 

 they now appear dry. There must, however, in order to make the 

 " head " effective, have once been a continuous column of water which 

 introduced the materials for cementation. It is at least difficult to 



