LOESS-DEPOSITING WINDS IN LOUISIANA 539 
reaching the low elevation. If the elevation were of small area, 
there might also be an accumulation of dust on the lee side of the 
obstruction, as snow drifts on the lee side of a tight fence; but in 
this case the winds passed over several miles of low upland, and it 
seems probable that most of the heavy load would be deposited on 
the windward side and but little dust would be left to accumulate 
on the leeward side. The loess on the Avoyelles Prairie is about 
12 feet thick at the southern end of the area and 6 to 7 feet thick 
at the northern end, a difference in thickness indicating southerly 
rather than northerly winds as the main depositing agents. No 
sections were observed which allow comparisons of thickness on the 
eastern and the western sides. About 40 miles east of north from 
the Avoyelles Prairie is Sicily Island, the southern extremity of the 
Bayou Macon Hills, which, as we have seen, is a loess-covered ridge 
extending from Arkansas into Louisiana. At the southern end of 
Sicily Island the loess is from 12 to 14 feet thick, and about 7 miles 
northward it thins to 7 to to feet. The evidence here is not so 
clear, for the dust may have accumulated on the lee side of the 
ridge from northerly winds, or it may have accumulated from the 
deposition by southerly winds at the southern side of Sicily Island. 
However, it seems that the thicker loess at the southern ends of 
both these elevations points to the greater effectiveness of southerly 
winds as loess-depositing agents as compared with northerly winds. 
PRESENT WINDS 
There is some interest in comparing modern wind directions to 
ascertain, if possible, whether the most effective modern winds in 
this region are at present westerly and southerly. Unfortunately 
no positive conclusions can be reached, because one cannot be sure 
that the average for so short a time as that for which we have 
records represents the modern wind directions, and, furthermore, 
the important elements of wind persistence and velocity are not 
given in the reports. Fig. 3 shows the average prevailing wind 
directions for the several months at New Orleans, Louisiana; Vicks- 
burg, Mississippi; and Memphis, Tennessee, for periods of thirty- 
six, thirty-five, and thirty-five years respectively. The winds at 
Vicksburg and Memphis are more significant than those at New 
