738 C. R. VAN HISE 



for instance, that the water entering at one point issues at 

 another point at the same elevation, after following a deep 

 underground path. Suppose the water during the journey comes 

 in contact with volcanic rocks, or suppose the water becomes 

 warmer as the result of the normal increase in temperature with 

 increased depth. We will suppose, for the sake of simplicity, 

 that the temperature of the water is o° C. where it enters the 

 ground, and at a temperature of 100° C. where it issues. This is 

 an extreme case, and beyond the facts ; but it makes the illus- 

 tration simple. During its journey the water expands as a result 

 of its rise in temperature, and a unit volume of the issuing water 

 weighs only about 96 per cent, as much as does a unit volume 



the entering water. The cooler or descending column con- 

 tains a greater mass of water than the ascending column ; it is, 

 therefore, pulled stronger by the force of gravity ; and conse- 

 quently circulation takes place. The descending column falls 

 and the ascending column rises because of the gravitative stress. 



In the case of the Chicago artesian wells we have seen 

 that the flowage is due to differential gravitative stress result- 

 ing from difference in elevation. In the case we have just con- 

 sidered, we have seen that the flowage is due to differential 

 gravitative stress occasioned by difference in temperature. 

 Therefore, underground water circulation caused by gravitative 

 stress may be initiated by difference in head or difference in 

 temperature, or by both combined. Ordinarily difference in 

 head and difference in temperature work together. Commonly 

 water enters the ground at a higher level than it issues ; and I 

 think it can be shown that water which is descending is, upon 

 the average, at a lower temperature than water which is ascend- 

 ing, although I cannot stop to fully discuss this point. There- 

 fore the descending column is heavier. Hence, unequal gravi- 

 tative stress, caused by difference in head and by difference in 

 temperature, is the adequate cause to which I appeal to account 

 for the circulation of underground water which does multifarious 

 kinds of geological work, a small part of which is the deposition 

 of ores. 



