LOESS IN THE WISCONSIN DRIFT FORMATION. 



Loess has long been known to cover the glacial drift of the 

 earlier ice epochs at various points, especially along the water 

 courses of the western portion of the Mississippi basin, and to 

 have more or less extensive development in like relation to val- 

 leys in extra-glacial territory both west and south of the drift. 

 It also occurs, especially along the Mississippi and its tributaries, 

 in the driftless area which lies in Wisconsin, Illinois, Iowa, and 

 Minnesota. 



In addition to its occurrence at the surface over the older 

 drift sheets, loess is known to occur between beds of till out- 

 side the area covered by the ice of the Wisconsin epoch. In 

 some places the surface of this buried loess is marked by a soil, 

 often of considerable thickness. These facts show that there 

 are at least two sheets of loess connected with the earlier sheets 

 of drift. The sheet of loess which overlies the lowan drift 

 often terminates abruptly, as a surface mantle, at the edge of 

 the Wisconsin formation, but frequently passes beneath it. 

 Outside the drift-covered country also there are, in some places, 

 two distinct beds of loess, the one above the other. ^ The sur- 

 face of the lower is often marked by a well-developed soil, and 

 furthermore shows, by its color and chemical condition, that it 

 was long exposed before the overlying mantle was deposited 

 upon it. 



The stratigraphical relations of the loess and drift, especially 

 when taken in connection with other considerations, seem to 

 point clearly to the conclusion that the loess had an intimate 

 connection with the drift in origin, and that there were at least 

 two epochs of loess deposition later than the first, and earlier 

 than the last, glacial epoch. The uppermost bed of extra-glacial 

 loess, where two are developed, seems to be capable of definite 



'Geological Survey of Arkansas, Ann. Rep. 1889, Vol. II, p. 233. 



929 



