THE LOESS OF SOUTHWESTERN IOWA 



717 



Underneath the red loess is the pebbly till of the Kansan drift- 

 sheet, which is here of the same general character as that everywhere 

 seen throughout southern Iowa. It is the usual rock mealjcharged 

 with erratics of every description; the uppermost three or four~feet 

 present the usual aspects of the ferretto zone so welljdescribed^by the 

 geologists of the Iowa survey. The color of^this ferretto approximates 

 closely that of the red loess above it, but^there is]never^the]^shghtest 

 difficulty in distinguishing the line of demarkation. /^ The leaching 



Fig. I. — Section in railroad cut at Red Oak, Iowa, showing the three deposits of 

 loess over the Kansan till. 



and oxidation which produced the ferretto have left it mottled with 

 white patches of kaolin, marking the site of former pebbles of feldspar. 

 It contains also numerous pebbles of quartzite, greenstone, and other 

 materials. Moreover, the exact line of demarkation is very fre- 

 quently indicated by a layer of gravel and pebbles which owes its 

 origin to the action of wind and weather on the long-exposed surface 

 of the till, whereby the finer particles were removed and the coarser 

 ones left behind as a mechanical concentrate. This phenomenon 

 is similar to that observed at the contact of the upper surface of the 

 lowan drift with the loess in the paha region of the eastern part of 

 the state. 



As shown in the railroad cuts within the city limits of Red Oak, 



