750 



SCIENCE. 



[N. S. Vol. XIV. No. 359. 



dreds of thousands of times as much water. 

 The vast quantity of water necessary can- 

 not be derived from the igneous rocks pres- 

 ent at a given time and place, although 

 they may have contributed a portion of it. 

 Bat it is held that the major portion of this 

 vast quantity of water could only have 

 been derived from the rainfall. My third 

 fundamental premise is, therefore, that the circu- 

 lating underground water is mainly of meteoric 

 origin. 



The question which now arises is the cause 

 of the flowage of underground water. Why 

 does it move? Until we know the force 

 which drives it, we cannot know the man- 

 ner in which it circulates. Geologists have 

 frequently appealed to the great energy of 

 the subterranean heat, due to depth or to 

 igneous rocks, to drive this water. But this 

 is not enough. How does this subterranean 

 heat act in producing this circulation ? A 

 few miles west of Denver are the crystalline 

 or core rocks of the Front Range. To the 

 east of these there is a series of sedimentary 

 beds, some of which are water-carriers, and 

 which dip below impervious strata. The 

 water rises to the surface at Denver. Why 

 is this so ? Simply because the water is at a 

 higher level where it enters the formations 

 than where it issues at the surface. The 

 force which drives the water is gravita- 

 tive stress. Gravitative stress is every- 

 where and all the time at work. The 

 longer column is pulled downward with 

 greater force than the shorter column. 

 The difference in the height of the two 

 columns is called head. Therefore, the 

 water in the longer column moves down- 

 ward, and that in the shorter upward. We 

 now reach my fourth fundamental premise : That 

 gravitative stress is the chief cause of the circula- 

 tion of underground water. 



The flowage of water in the Denver arte- 

 sian basin does not require the force of the 

 subterranean heat below. But there is a 

 way in which the subterranean heat can 



promote the circulation of underground 

 water ; and, indeed, does. This is by heat- 

 ing it. When the water is heated as a re- 

 sult of the contact with igneous rocks, or 

 heated because it penetrates deep into the 

 earth, it expands. If it expands unequally, 

 as it is likely to do, one column may become 

 lighter than the other, even if they are of 

 the same height. If so, circulation would 

 be set up. This is the principle of hot- 

 water systems of heating buildings. The 

 heat of the fire expands the water and forms 

 two columns of unequal density. Under 

 this condition of affairs gravity pulls the 

 denser column harder, and a circulation 

 takes place. Therefore, the heat of the 

 igneous rocks acting upon the underground 

 solutions, or the heat of the rocks due sim- 

 ply to depth, provided the circulation be of 

 sufficient speed, may result in flowage. 

 Thus there are two causes which result 

 in the underground circulation, which 

 may work separately or together — (1) 

 head, and (2) variable temperature. But 

 in either case continuous movement of the 

 water in a definite direction, or its circula- 

 tion, is due to gravitative stress. 



Therefore, we have these four funda- 

 mental premises : (1) The chief class of ore 

 deposits is segregated by underground water; 

 (2) the source from which the water derives the 

 metals is the zone of fracture; (3) the circu- 

 lating underground water is mainly of meteoric 

 origin; (4) the force which drives the water in 

 its circulation is gravitative stress. 



It is now necessary to consider in some 

 detail the manner in which underground 

 water moves. For a long time I have 

 realized that if underground water had a 

 difference in head it might penetrate to 

 a great depth and rise again to the sur- 

 face ; but I did not realize that it was not 

 necessary to assume exceptional openings 

 for such a circulation. I assumed that 

 where such a circulation took place excep- 

 tionally favorable channels were available ; 



