538 F. V. EMERSON 
percentages of these minerals in the western belt are due to a dif- 
ferential selection of wind load. The weaker easterly winds carried 
a relatively finer load than the stronger westerly winds, with the 
result that higher percentages of lime, potash, and phosphoric-acid- 
carrying minerals were deposited in the western loess belt. 
3. The third line of evidence concerns the effectiveness of 
northerly winds as compared with southerly winds as loess-carrying 
agents. The Avoyelles Prairie (see Fig. 2) is an island-like area of 
50 miles 
eeSreily Island: 
: / shane 
eLakeCharles  -*.2: 
J 
Fic. 2.—Map showing the loess belts (dotted) in Louisiana and Mississippi. 
(Loess in Mississippi after Mississippi Geological Survey.) 
about 80 square miles, which is entirely surrounded by alluvium 
and capped by a layer of loess overlying Lafayette-Columbia and 
Port Hudson materials. ‘The platform on which the loess rests is 
10 to 15 feet above the alluvium in the two places where the top 
of the platform was observed. This relatively elevated area was 
exposed to the sweep of the winds from all directions, with no 
loessial soil within ro to 30 miles, and it seems clear that the preva- 
lent winds would deposit the thickest loess in a manner analogous 
to the drifting of snow in some regions. ‘The loess-bearing winds 
from the south, for instance, would drop a portion of their load on 
