A PHENOMENON OF THE KANSAN DRIFT IN NEBRASKA 809 



etc., according to the component materials. Perhaps, as has been 

 suggested, these are Aftonian. 



Incident to the protracted frigidity of a glacial period is the 

 freezing of soils, sands, and gravel to the rigidity of rock (frigite). 

 Any natural force which could rend and transport rock could rend 

 and transport the rocklike soils and sands. Continental glaciers 

 are powerful graders and levelers. They act resistlessly upon 

 rock and frozen soils and sands, breaking them into blocks and 

 transporting them long distances southward. The load of rocks 

 and frozen blocks is finally dropped by the melting ice, and buried 

 in glacial mud. The blocks are thus preserved in their integrity. 

 A stream bed, or coulee, could in a like manner be frozen, sub- 

 sequently broken into sections, transported, and deposited. 



The term ''^glacial drift" as used in an unfortunately restricted 

 and local sense in Nebraska refers to that particular portion of the 

 Kansan drift, which is rendered conspicuous by coarse pebbles 

 and bowlders of reddish Sioux quartzite. This layer is pretty 

 generally recognized, and though it may be but a foot or two in 

 thickness it is often expedient to speak of it popularly as "the 

 drift." In a broader sense, however, our drift also includes, though 

 less obviously, extensive beds of glacial clay, generally spoken of 

 as joint clay, which may reach fifty feet in thickness. It has long 

 been said facetiously by eastern geologists that the glacial deposits 

 of Nebraska are ''buttered on so thin that one cannot tell the 

 buttered side." It is probable, however, that this bit of good 

 humor would never have become classic had our drift not been 

 confounded with our loess. There may be recognized an older, 

 bottom layer of a dark, or even black color (sub-Aftonian, Jerseyan, 

 or Nebraskan), and a younger, top layer of a lighter color, generally 

 of a yellowish or reddish cast (Kansan), neglecting any Aftonian 

 sands and gravels. The frigites herein described are confined 

 to the Kansan drift. 



It so happens that the drift often resembles the loess so closely 

 that they run together, and seem to be terms in the same series. 

 At times it puzzles even those who are experienced to distinguish 

 between them. The southeastern half of Nebraska has for con- 

 venience been generally figured as one continuous loess sheet. 



