ARTESIAN WELLS OF SOUTH DA 



KOTA. 



By Prof. J. E. TODD. 



The great flowing wells of South Dakota have attracted a world- 

 wide interest. They stand unrivaled in the height of their pressure 

 and the copiousness of their flow. The display of their power is so im- 

 pressive that many have thought that some force not yet understood 

 must be found to explain them. To one, however, familiar with the 

 geology of the region and the common laws of hydraulics the principal 

 facts are easily understood. 



The immediate sources of the flowing waters are the different 

 layers of sand or sandstone in the lower portions of the Cretaceous 

 which with the intervening beds of clay comprise the so-called Dakota 

 formation. Below it, also, and not clearly distinguished from it, are 

 similar beds belonging to the Jurassic age. From these two forma- 

 tions, and mainly from the first, all. the larger and deeper wells of Da- 

 kota derive their supply. The water comes up often with an immense 

 power, 175 to 200 pounds per square inch. Why should it not have 

 ere this burst forth and spent itself ? The reply is that 400 to 1,000 

 feet of compact, heavy clay have been sufficient to hold it down. 

 There are nevertheless a few places where natural breaks have 

 occurred as along the Missouri river near Chamberlain and probably 

 near Yankton and along the James river in Hutchinson county. 



But our inquiry contemplates the original sources of the water. 

 Whence does the rock receive its copious floods? The Dakota forma- 

 tion if considered by itself resembles a huge shallow trough extending 

 indefinitely north and south, underlying the great plains. Its western 

 edge of very irregular form lies exposed as foot hills along the eastern 

 base of the main chain of the Rocky Mountains, also in similar ridges 

 around the principal clusters of mountains further east. These Expos- 

 ures lie in an altitude of from 3,500 to 6,500 feet above the sea. Its 

 eastern margin thins out to a ragged edge and is almost completely 

 buried under later formations mainly by the boulder clay of the drift. 

 It lies at an altitude of from 800 to 1,200 feet above the sea. Its upper 

 portions are exposed along the Missouri river from Sioux City south- 

 ward. With this conception one will readily understand, I think, how 

 if water is turned into the porous substance of the formation until it is 

 nearly filled to the top of its western edge, that if it is tapped from 

 points of the surface only 1,300 feet above the sea as is the case in the 



