296 The American Geologist. November. 1902 
ated primarily in the drift. In the north it was loosened and 
sifted out from the coarser material by rain, by wind, by bur- 
rowing worms, insects, mammals, etc., and bv scratching birds, 
and to some extent by growing plants, while its volume was 
increased by the chemical decomposition and disintegration of 
the coarser materials thus exposed.^'' 
Some of this material was washed into the streams, and 
some of it was (and is) blown about by the winds. In the 
southern Mississippi valley, where there is no glacial drift 
and vet an abundance of loess, the material of the loess was 
probably all brought down by the great river, and chiefly by its 
^Missouri branch. During the summer months our streams 
reach their lowest levels. Great bars of sand and mud are 
therebv exposed to the dessicating influence of sun and wind. 
During the summer, too, strong winds sweep along their val- 
leys and gather up the fine material so exposed, t 
With it also mingled more or less of the finer material gath- 
ered by the wands directly from higher grounds, and perhaps 
with calcareous particles from fluviatile shells w^here present 
in the streams, but the main supply in the south and perhaps in 
large part elsewhere where loess was formed, was obtained 
from the bars of the stream. 
2. The agency. — The objections to water and ice as 
agencies of transportation have already been briefly stated. 
Wind does carry large quantities of material, and in the loess 
regions winds are strong and frequent during the summer sea- 
son Avhen the soils are loose and easily eroded. ^Moreover, the 
general southerly course of the larger streams in the ^^lissis- 
sippi valley, along which most of the loess is deposited, favors 
the concentration of the prevailing southerly winds in the 
troughs of the valleys, through wdiich they crowd with in- 
creased force, and dislodge the fine particles of detritus 
brought down by the streams and exposed in bars. In the 
north drifting snows, especially in the ^Missouri river region, 
also gather up and carry great quantities of dust. 
3. — The anchorage. — The material so gathered up must be 
deposited in a place from which it cannot easily be dislodged by 
*That finer material is thus removed and the coarse material so con- 
centrated near the .surface has already been observed. See Proc. la. Acad. 
Sci., vol. IV. p. 70. 1S97: etc. 
iFor di.scussion of the probable amount of this material see Jour. 
Geol vol. VII, p 135.— 1S99. or Proc. la. Acad. Sci., vol. VI, pp. 109 and 
110.— 1899. 
