VISCOSITY AND DEPTH OF CIRCULATION. 579 



the same average rate as between 0° C. and 90° C, at a depth of 9,000 

 meters, where the temperature is probably about 300° C. greater than at 

 the surface, the viscosity would be only about one-twentieth of that at the 

 surface. From the foregoing it appears that in capillary ojoenings in the 

 part of the zone of fracture below 1,350 meters, with a given head, the 

 flowage of water for capillary tubes of a definite size would vary from 

 about three times to about twenty times faster than at the surface. These 

 numbers are not accurate, because water at the surface usually has a higher 

 temperature than 0° C, but the error is not so great but that the conclusion 

 follows that increase of temperature with depth is a very important factor, 

 tending to promote a circulation in the deeper parts of the zone of fracture, 

 for water follows the lines of least resistance; therefore, ground water, on 

 the averag'e, follows a deeper path than it would were the temperature and 

 viscosity uniform. 



. RELATIVE LENGTHS OF VERTICAL AND HORIZONTAL COMPONENTS. 



The vertical component of the journey of ground waters in the belt of 

 cementation may be considered as confined to the zone of fracture, and is 

 probably measured by 10,000 meters, or at most by 12,000 meters. The 

 lateral component, on the other hand, maj vary from a few meters to 

 hundreds or even a thousand or more kilometers. There can be little doubt 

 that, on the average, the horizontal component is much greater than the 

 vertical component. No limit can be assigned to the horizontal movement 

 of water. It is known that the nearest source for artesian waters may be 

 many kilometers from the wells. For instance, in the James River Valley, 

 Dakota, the Dakota sandstone yields abundant water. The nearest place at 

 which this sandstone outcrops is several hundred kilometers distant, and it 

 therefore appears highly probable that the horizontal movement of the 

 ground water is measured by hundreds of kilometers, while its vertical 

 journey is probably less than 1,000 meters. Doubtless in this case the 

 horizontal distance which the water has journeyed is far greater than the 

 average, but still the average journey is probably one of considerable 

 length. 



The length of the horizontal component of the journey has much to do 

 with the depth of the circulation. Where the horizontal component is 



