102 
The American Geologist. 
February, 1896 
The Relation between Ice-lobes south from the Wisconsin Driftless 
Area. Frank Leverett, Denmark, Iowa. Instead of a coalescence of 
ice-lobes from the east and the west sides of the Driftless Area in the 
drift-covered district to the south there was an invasion and withdraw¬ 
al of one lobe (the western) before the other reached its culmination. 
The eastern lobe encroached upon territory previously glaciated by the 
western, depositing- a distinct sheet of drift and forming at its western 
limits a well-defined morainic ridge. There appears to have been a 
period of considerable length between the withdrawal of the western 
lobe and the culmination of the. eastern. 
Subsequently, however, there was a readvance of the lobe on the 
west into northeastern Iowa, and this re-advance appears to have been 
contemporaneous with the nearly complete occupancy of northwestern 
Illinois bv the eastern ice-lobe. It seems not improbable that the ice- 
lobes were then for a brief period coalescent for a short distance about 
the south border of the Driftless Area. Evidence of complete coale¬ 
scence, however, is not decisive so far as yet discovered. 
These developments serve to throw light upon the cause for the scar¬ 
city of lacustrine dejiosits in the Driftless Area. They show that there 
was at most but a brief period in which the southward drainage of the 
Driftless Area was completely obstructed by the ice-sheet. 
By means of maps it was shown that there were.probably two centers 
of chief snow accumulation and glacial outfibw,—one, predominant the 
earlier, being in the area between Hudson bay and the Rocky moun¬ 
tains ; and the other, later predominant, on the Laurentide highlands 
and the Labrador plateau. 
Prof. Salisbury, in discussion, remarked the great complexity of the 
Glacial period: and Prof. Wright, while admitting its complexity in 
details, emphasized its essential grand unity. 
Prof. Shaler directed attention to the importance of demonstrating 
the progress of glaciation from west to east, because, if the sequence of 
events can be established, we thus advance far toward discovering their 
causes.* 
The Loess of western Illinois and southeastern Iowa. Frank Lever- 
ett. The north border of the loess both in western Illinois and eastern 
Iowa appears to have been determined by the ice-sheet. The loess is 
apparently an apron of silt spread out to the south by water issuing 
from the ice-sheet. It is loose textured at the north and becomes finer 
textured toward the south, showing a decrease in the strength of depos¬ 
iting currents. The wide extent of the loess over the Uplands has led 
to a consideration of the influence of wind as well as water in its distri¬ 
bution. It is thought that wind-deposited loess may be distinguished 
from that which is water-deposited. The wide extent, however, appears 
to be due to water distribution rather than wind. Wind action appar- 
*Compare Am. Geologist, vol. xiv, pp. 62-65, July, 1894; and two ar¬ 
ticles, with maps showing stages of recession of the ice-sheet, in vol. xv, 
for May, 1895, and vol. xvi, for August, 1895. 
