146 



the west side of the valley, are problems whir-h we hope to attack in the 

 future. 



The margin of the east bluff is cai.petl by a broad ridge of sand, stand- 

 ing 20 to 30 feet al)ove the general level of the till plain to the east of it, 

 and exhibiting in many localities characteristic eolian topography. The 

 surface sands are underlaid by loess, and the whole deposit is interpreted 

 as having been blown up by westerly winds from the valley below. 



The small streams from the east which break through the bluff have 

 wide flat-floored valleys opening upon the terrace with accordant grades. 

 In their natural state, none of them ever extended their channels across the 

 terrace to the river. Their waters, ponded in depressions between the bars, 

 sunk into the sand or evaporated. The depressions are generally puddled 

 vv-ith a thin coat of lacustrine silt. 



