Mathematical a}id Geological Papers. 61 



Glacial epoch, when the rivers received sufficiently high veloci- 

 ties through the elevation of northern lands, we have in this 

 work of excavation, especially, a time measure of some value. 

 At the rate of one foot in five thousand years, the work of 

 excavating valleys one hundred feet deep would have taken 

 five hundred thousand years, or approximately one-half of the 

 time from the beginning of the Glacial epoch to the present. 

 It should be remembered that only the northeastern portion 

 of Kansas was invaded by glacier ice, that of the Kansas 

 glacier, and the balance of the state was being denuded all the 

 time by the atmospheric and aqueous agencies. So during all 

 of the Glacial epoch in most of the state, and during the major 

 portion of the time in the glaciated part, the rivers with plenty 

 of water of high velocity deepened and broadened their valleys 

 to near their present depth. At that time the floor of the 

 valleys must have been covered with a layer of chert gravel 

 from three to five feet thick, composed of the debris of the 

 Wreford and Florence limestones, together with the flint 

 (chert) weapons used by the aborigines of Kansas. 



East of the sixty-mile-wide belt covered by the residuum of 

 the "Flint Hills" are still other chert gravels derived from the 

 Oread and Dennis limestones, and still farther east, mostly in 

 Missouri, are the abundant chert gravels derived from the 

 Mississippian limestone. 



During the Champlain epoch the previous up-warping of the 

 (ilacial epoch was reversed, and the northern lands sank to a 

 level of from three hundred to one thousand feet, according 

 to Dana, below that possessed at present. This subsidence 

 caused the south-flowing rivers to become sluggish and to de- 

 posit sediment rapidly. The Neosho, Cottonwood, Verdigris 

 and Fall rivers, and probably other streams in the "Flint Hills" 

 gravel belt, buried the chert gravels to a depth of twenty or 

 more feet with river silt, but with increasing slowness as the 

 bottoms increased in height. 



During the Recent epoch the northern lands have recovered 

 in part the elevation they possessed during the Glacial epoch ; 

 the rivers have increased their velocity and are again cutting 

 into the rock strata. The rivers so rarely overflow their 

 banks at the present time that the bottoms are scarcely holding 

 their own in the struggle for existence. The tree stump at 

 Council Grove showed no burial of its roots by silt, and its 



