<)0 Minnesota Academy of Science 



clear to us now when, if instead of the descriptive term "greater 

 age" of drift we use the up-to-date term pre-Kansan (Nebras- 

 kan ), and instead of "the great drift sheet" we say Kansan drift. 

 The "inter-glacial epoch" is the Aftonian now. In short, Win- 

 chell discovered and described, at that early date, the differences 

 between those two "older drift" sheets, which are now recognized 

 under the names pre-Kansan and Kansan. 



The drift "of the last glacial epoch," as distinguished from 

 the '"older drift," was described by Prof. Winchell (loc. cit. p. 

 544, 581), in writing of the geology of Rock and of Brown 

 counties, and it is made quite clear, incidentally, in that way, that 

 he looked upon the greater part of the state as a young drift 

 covered area. In writing of the glacial drift sheets in Dakota 

 county (Final Report, Vol. 2, pp. 86-88), the red drift, which is 

 found there, is well described and interpreted. He says in one 

 sentence that "the later gray till lies on the later red, but the 

 latter lies on the older gray" (p. 88), i. e., the older drifts as 

 described formerly in Fillmore county are here called "older 

 gray," and the "latest drift," as formerly called, is now called 

 "younger gray." A "red drift" which lies between those two 

 is classed and described as "younger red,"- — as if quite contem- 

 poraneous with the "younger gray." His conclusion was correct. 

 The younger gray and younger red are of course the Wisconsin 

 drift sheets, according to our present nomenclature. 



The method employed by the State Survey, of describing 

 the state's geology piece meal — county by county — of course, had 

 this disadvantage, that the geologist had rather too many local 

 details to record and moreover could not well discuss gen- 

 eral principles without getting beyond the limits of the county. 

 That must explain why it is necessary to turn from one county 

 to another to find N. H. Winchell's general knowledge of the 

 glacial drift. The same disadvantage, of course, applies to the 

 work of others of the survey and explains, in part at least, why 

 they did not take up and advance the most important of Win- 

 chell's ideas on the drift here in Minnesota. As it is, that work 

 was done elsewhere and is now brought in, so to speak, from 

 Illinois and Iowa to be applied here. Instead of Prof. Winchell's 

 old gray drift, young gray drift, red drift, etc., we thus have 

 borrowed terms, Kansan, Illinoisan, Wisconsin. 



