20 The American Geologist. J"'^'- I'^oi- 
THE AGE OF THE KANSAN DRIFT SHEET. 
By OscAK H. Hehshev, Berkeley, California. 
Although somewhat belated and subject to the generalizing 
effect of impressions dimmed by time and the vicissitudes of 
rough life in a mining camp, I desire to add my quota in sup- 
port of the proposition that the Kansan drift sheet of th^ Mis- 
sissippi basin is a very old one. For some years I have been in 
the ranks of those who maintain that the earlier glaciations of 
the Upper Mississippi region occurred long prior to the last or 
Wisconsin, but it is only recently that I have come to appre- 
ciate the significance, of the evidence. 
The "earlier drift" of northwestern Illinois is manifestly 
so much older than the lowan drift, that it was for some years 
correlated with the Kansan sheet of southern Iowa, [Missouri 
and Kansas. Being surrounded by impressive evidences of 
the aged condition of the former, I was somewhat skeptical 
of the existence anywhere in the Mississippi basin of a drift 
sheet which could be proven to be of yet greater age than it and 
was not inclined to approve suggestions that the old drift of 
northwestern Illinois was more recent than the Kansan and 
probably a portion of the then latelv discriminated IlHnoian 
sheet. 
In the summer of 1899, while on a. pedestrian trip from 
Freeport, in Illinois, to Mena, in Arkansas, I took occasion to 
visit Mr. F. Leverett at his home in Lee county, Iowa, and he 
conducted me across the broad smooth ridge which bounds 
the Illinoian drift and on to the Kansan area to the west. It 
was in this region, I believe, that Chamberlin first recognized 
the significant difference in topography of the two sheets now 
known respectively as Illinoian and Kansan. and his interpre- 
tation has been ably supplemented by the investigations of 
Leverett, as well as by detailed investigations by the Iowa 
Geological Survey.* Mv conversion to their opinion was 
rapid and complete. Subsequently this was re-enforced by 
observations in northeastern Missouri where the Kansan drift 
sheet and its attendant erosion topographt are typically devel- 
ooed. 
*A fnller discussion of this subject is contained in Mr. Leverett's report on 
the "Ulinois Glacial Lobe," forniing Monograph XXXVIII of the U. S. Geol^ 
Survey. 
