142 A TREATISE ON METAMOEPH1SM. 



the larger masses of ground water the viscosity of water and the friction 

 becomes almost zero per unit area. Evidence of this is furnished by the 

 fact that artesian water flowing through rocks for hundreds of kilometers, 

 the openings of which are capillary, may have nearly the full pressure due 

 to head. For instance, the artesian water adjacent to Lake Michigan at 

 Chicago at the early wells, before they became so numerous as to interfere 

 when allowed to flow, had a head of 30 meters above the surface, and the 

 feeding area is onty about 80 meters above Chicago;" yet the water has 

 traveled underground from 150 to 250 kilometers. The resistance causing 

 the loss of head of 50 meters is to be distributed through this distance; 

 therefore the friction per meter must have approached an infinitesimal 

 amount. The same thing is again finely illustrated by the artesian wells 

 of the James River Valley of South Dakota. The water of these wells 

 must have traveled at least from the eastern border of the Black Hills, 400 

 kilometers. The elevation at the source is 1,500 meters and at the James 

 River 500 meters. The consequent loss of head of considerably less than 

 1,000 meters is due to resistance through the entire distance, and again must 

 be almost immeasurably small per meter.'' In all such instances the average 

 movement is exceedingly slow, for it will be shown that to accomplish the 

 first of the above journeys more than a centuiy was perhaps required, and 

 for the second possibly centuries were necessary. (See pp. 585-586.) 



But the moment the speed of movement becomes appreciable the resist- 

 ance promptly runs tip. This is shown by the very slow fall of a slanting 

 water table in sands as the result of lateral flowage. The best illustration of 

 this of which I know is that kindly furnished me by J. B. Lippincott, city 

 engineer, of Los Angeles, Cal. The Los Angeles River is mainly fed by 

 ground waters derived from granitic and other sands which are of moderate 

 coarseness, but the openings of which are capillary. The water table 

 rises from the headwaters of the river to a point north of Fernando — about 

 16.1 kilometers — from a little more than 180 meters to a little more than 

 330 meters, or 9.3 meters per kilometer. Mr. Lippincott says that from 

 1896 to 1900, inclusive, five years, there was practically no rainfall, and 



"Leverett, Frank, The water resources of Illinois: Seventeenth Ann. Rept. U. S. Geol. Survey, 

 pt. 2, 1896, pp. 805-806, 811. 



&Darton, N. H., Artesian waters of the Dakotas: Seventeenth Ann. Eept. U. S. Geol. Survey, 

 pt. 2, 1896, pp. 665-670, pi. lxx. 



