648 RECORD OP MEETINGS OF THE 



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

 for example, is flatly opposed to our experience in those hith- 

 erto few but yearly increasing deep mines which go below 

 1,500 or 2,000 feet. Wherever deep shafts are located in regions 

 other than those of expiring but not dead volcanic action, they 

 have passed through the ground-water, 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 W. Finch, 

 recently the State Geologist of Colorado, has reached the con- 

 clusion after wide experience with deep mines that the ground- 

 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 mate- 

 rials for cementation. It is at least difficult to understand 

 how a process which could only progress by the introduction 

 of material in very dilute solution should by the agency of 

 crystallization drive out the only means of its production. 

 Some residue of water must necessarily remain locked up in 

 the partially cemented rock. This residue we, of course, do 

 not find where rocks are dry and drifts are dusty. In many 

 cases also, where deep cross-cuts have penetrated the fresh 

 wall-rock of mines, cementation if present has been so slight as 

 to escape detection. 



If we once admit that this conclusion is well based, it removes 



