14 THE 1EEIGA TION A GE 



i 



half finds its way into these porous strata, it would furnish 83.635,200,- 

 000 cubic feet per annum. Col. Nettleton reported some time since 

 that the Missouri river loses 834 cubic feet per second where it flows 

 over the Dakota formation at Great Palls, Mont. It seems reasonable 

 to suppose that from the North Platte, the Big Horn and the Yellow- 

 stone, there may be twice as much more derived. If we allow the 

 score or more of smaller streams around the Black Hills and the Big 

 Horn Mountains to offset the possible overestimate, we would still by 

 this calculation have 77,103,072,000 cubic feet furnished in addition. 

 This would afford water sufficient to supply more than ten times that 

 at present derived from all the artesian wells in South Dakota. More- 

 over, if, as seems to be very probable, the rainfall sinking into the 

 older formation makes its way eventually into the Dakota and Jurassic, 

 and if we estimate that one-fourth of the total rainfall upon their ex- 

 posed surface is so transferred, we may reasonably double the amount 

 given above. Besides these annual supplies there is what may be 

 called a stored supply, which has been accumulated in the water-bearing 

 formations at such an altitude above the mouth of the wells that should 

 the regular supplies cease it would sustain the flow of the wells for 

 considerable time. From the map and section subjoined it may be 

 readily seen that extensive areas in Montana and Wyoming may lie at 

 an altitude sufficient to accomplish this result. Since the water- bear- 

 ing layers of the Dakota and Jurassic have an average thickness of 300 

 feet and the sand may contain at least one tenth of its volume of water, 

 it would represent an equivalent to a lake 30 feet in depth extending 

 over the whole area underlaid by these formations. Of course over 

 most of the region so underlaid it would be obtained only by pumping, 

 but ezery square mile lying at an altitude higher than the surface of 

 the James River Valley might contribute through the wells, water 

 sufficient to cover a square mile in the James River Valley one foot 

 deep per year for thirty years. 



In order to verify these calculations many and difficult observa- 

 tions extending over wide regions and for a series of years will be 

 necessary. It is hoped that the United States geological survey and 

 that of South Dakota may undertake to place our knowledge concern- 

 ing this most important supply upon more reliable basis as soon as 

 practicable. 



Concerning the permanence of the supply, we call attention to the 

 following facts: Although the supply is doubtless capable of being 

 exhausted, if too mrny wells are sunk, there is abundant reason for 

 believing that it is much less so than most natural resources. Water 

 is not destroyed by its use and its supplies are constantly accumulating. 

 Its deposits are from the nature of the case more easily calculated and 

 its decline more easily observed and more certainly determined. 



