146 
the west side of the valley, are problems which we hope to attack in the 
future. 
The margin of the east bluff is capped by a broad ridge of sand, stand- 
ing 20 to 30 feet above 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 interpreteé 
as having been biewn un by westerly winds from the valley below. 
The small streams from the east which break through the bluff have 
wide fiat-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 
with a thin coat of lacustrine silt. 
