ISSUING WATER TRANSPORTS HEAT. 591 



i.ie transmission of their heat to the surrounding rocks and by conduction 

 to the surface, but the underground circulating water in contact with the 

 igneous rocks and in contact with the other rocks heated by them absorbs 

 a large amount of the heat, probably a much larger amount than that 

 transmitted to the surface through conductivity. 



(4) After the water joins the sea of ground water its vertical com- 

 ponent is at first downward. Because of the normal increment of increase 

 of temperature — 1° C. in 30 meters — the descending water gradually 

 absorbs heat from the rocks. During the ascent the water tends to give 

 heat to the rocks, because it is passing from rocks of higher to those 

 of lower temperature. But the upward movement of the water is of 

 shorter duration, is in larger openings, and is more rapid than its downward 

 movement (see pp. 582-584); therefore it seems probable that in conse- 

 quence of- normal increase of temperature due to depth, more heat is trans- 

 mitted to the water than is abstracted from it. 



When we combine all four of these factors it follows to a certainty 

 that the water in its journey absorbs heat, on the average, and therefore 

 issues from the belt of cementation at a higher temperature than it enters it. 

 Hence it appears perfectly clear to me, from general reasoning, that during 

 the circulation of ground water it abstracts heat from the rocks. 



So far as I know, no attempt has been made to prove this general 

 statement by observation ; but it appears to be highly probable that it could 

 be proved by careful experiments. At the crests of elevations in various 

 regions temperatures should be taken at the level of ground water. In the 

 same regions the average temperature of the water issuing from springs 

 should be observed. The two sets of data should be compared. While no 

 general observations have been made along these lines, in some regions of 

 recent orogenic movements and volcanism observation does clearly show 

 that the temperature of the issuing water is higher than that of the entering 

 water. This is well illustrated by the Cordilleran region of western United 

 States. This is a region of comparatively recent epeirogenic and orogenic 

 movements and of volcanism. Gilbert and others" have shown that, 

 scattered throughout this vast region, occupying nearly one-third of the 



"Gilbert, G. K., Volcanic rocks and mountains, with localities of thermal springs in the United 

 States: TJ. S. Geog. Surv. W. 100th Mer., vol. 3, 1875, pp. 145-155. Howell, E. E.. Thermal springs: 

 ibid., pp. 256-257. Stevenson, J. J., Mineral springs: ibid., pp. 478-487. 



