264 Gould — Tertiary Springs of Western 



of the bed and the amount of water it contains. But if the 

 gravel bed extends to a considerable depth below the surface, 

 the water, still seeking its lowest level, will continue to 

 descend until in order to reach a steady flow wells must pene- 

 trate to a great depth. Happily on the plains this condition 

 is not usually met with. The thickness of the Tertiary strata 

 will perhaps average not more than fifty feet. In many 

 places, it is true the rock is as much as 300 feet thick, but 

 ordinarily this is not the case. The underlying stratum is 

 usually either Cretaceous or Permian. In either case the 

 lower rock is impervious to water. The water-bearing gravels 

 lying on the impervious ledges soon become saturated and the 

 water will often rise many feet in the bed, sometimes in fact 

 nearly to the surface. A well, then, to reach a steady flow 

 need only to penetrate to the saturated gravels. From this it' 

 follows that the wells throughout the region of the Tertiary 

 have as a maximum depth the thickness of this formation, and 

 as a minimum the distance to the saturated sand and gravels. 

 The thickness to which the saturation extends depends upon a 

 number of factors. Prominent among these are the slope of 

 the beds, the regularity of the underlying strata, the amount 

 of rainfall and the relative coarseness of the material which 

 carries the water. Of course there are a number of others but 

 they need not be considered in this connection. 



The water that I have just been considering is the under- 

 flow or " sheet water " of popular phrase. Thousands of wells 

 in western Kansas and Oklahoma obtain a never failing supply 

 from this source. A popular but erroneous idea prevails in 

 many localities that a subterranean lake is present or even that 

 an underground river is flowing toward the sea. It is obvious 

 that these explanations have no foundation in fact. 



The statement was made above that many of the streams of 

 the region have carved out a channel in the Tertiary and in 

 many instances into the underlying formations. This is true 

 at least in part for the following streams : Solomon, Sappa, 

 Prairie Dog, Saline, Smoky Hill, Walnut, Pawnee, Arkansas, 

 Ninnescah, Medicine, Bluff, Cimarron, Salt Fork, Beaver, 

 Wolf, Canadian, Eagle Chief, and Red Piver, with their 

 numerous tributaries. The greater part of these streams either 

 take their rise in the Tertiary or else rising beyond, flow across 

 this formation for a considerable distance. In almost every 

 case they have cut down into the subjacent rocks, often hav- 

 ing carved out canyon-like valleys in them. A person stand- 

 ing on the level Tertiary plain at a distance from the edge of 

 the valley may often be able to look across to the plain beyond 

 without being aware of the intervening valley. In other 

 instances the valleys are broad and shallow, being nothing but 





