34 C. R. Keyes — Loess Mantle and Kansan Drift-Sheet. 



reason of the fact that continental terranes of eolic origin have 

 been little understood. That the real nature of the deposits in 

 question was not inductively established long ago is due largely 

 to the circumstance that they were invariably approached from 

 the side of moist-climate conditions instead of from the side of 

 aridity. 



Fig. 1. 



,,■ Post -Gl acial toest 



Rans an Loess 



<^T^< ~i£ ^: j^q ^ 



•^Jertiaxy Loess 



I, I TTH ' ■ Hj j ..^ ,^, 



^C 



It is quite probable, therefore, that towards the Missouri 

 River the Plains deposits represent (1) a Tertiary lcess-section 

 of indeterminable thickness, (2) an extensive Pre-Kansan loess 

 which also once covered the country east of the river, but of 

 which few traces now remain on account of its profound dis- 

 turbance by the advance of the ice-sheet, (3) a loess-sheet 

 equivalent to the Kansan drift that is doubtless everywhere 

 near the glacial border quite thin, (4) an extensive Post-Kansan 

 loess, which is well developed west of the river covering the 

 surface of the entire region, passing eastward over the Kansan 

 drift-sheet, interlocks with the other drift-sheets in central and 

 eastern Iowa, and continues at the present time to form as 

 rapidly as loess has ever formed in the past. The several rela- 

 tionships are graphically represented in the accompanying dia- 

 gram (fig. 1). 



Des Moines, Iowa. 



