The Columbia Formntion in X. W. Illinois. — Herahey. IT 
CoURELATIOX WITH ADJOINING GlACIAL DkIFT. 
The character of the Vallej'^ loess, as noted in the Pecaton- 
ica basin, points to an origin of its material from the lower 
part of the valley towards the east. As the material is un- 
doubtedly glacial silt, we naturally look in that direction for 
some evidence that an ice-sheet or continental glacier lay near 
to the loess-depositing waters. It is now believed that such 
evidence has been discovered, and I will endeavor to present 
such portion of it as is known to me. 
The irregular line mentioned as bounding the Upland loess 
on its eastern side verj'^ nearly coincides with the terminal 
line of a distinctive drift sheet.* This drift is distinguished 
from the very ancient sheet to the west of it by (a) a very 
much fresher appearance: (6) less oxidation and less depth of 
leaching; (c) a discordance between the gravel ridge (esker) 
sj'-stems of the two sheets; [d) a discordance in the direction 
of glacial movement, and, in the Pecatonica valley, in the 
trend of the terminal lines of the two ice-sheets when they oc- 
cupied the same relative positions; (e) a very much different 
topography, the country underlaid by the western or ancient 
drift having that of a slightly glaciated region, and the coun- 
try underlaid by the newer sheet having that of a more ad- 
vanced stage of glaciation ; (./') the newer sheet is several 
times as heavy as the old, this difference being especially con- 
spicuous along the boundary; (y) the presence of slight but 
distinct morainic features east of the line, especially along 
the outer edge of the newer sheet; {h) very much less sub- 
aerial erosion on the drift east than on the ancient sheet west 
of the line; (/) the fact that the newer drift is near its edge 
overlaid by Upland loess, without any soil or. other evidence 
of land surface between, while the drift to the west shows de- 
cided manifestations of a long interval between the formation 
of the drift sheet and the overlying loess. 
The relations of the loess to this newer drift sheet are well 
shown in the Pecatonica valley. It has already been stated 
that the terrace formed by the Valley loess runs down the 
north side of the valley to about the mouth of Sugar river. 
*The existence of this drift sheet, as distinct from the older drift to 
the west, was first pointed oiU to tlie writer by Mr. I. M. liuell, of Be- 
loit, Wisconsin, wlio also rioted the fact that it bounds the loess on its 
eastern side. 
