Eskei's of the Kansan Epoch. — Hemheij. 251 
very large amount of work will be required jet before any 
dependence can be placed on a computation based on this 
principle. 
Terminal Lines in the Pecatonica Basin. 
On the map facing page 198. I have endeavored to roughly 
indicate the positions of some of these supposed terminal 
lines. In mapping margin No. 1, which is the outer drift 
margin, I have followed Chamberlin and Salisbury, Leverett, 
and Buell, with a few modifications due to personal observa- 
tion. Margin No. 2 may seem questionable, but from the 
facts that the '•special areas" which indicate it are the most 
western in their respective belts, and, when favored by the 
presence of valleys, are well developed, I am certain that they 
indicate a terminal line, although not a very important one. 
The problem lies in their correlation. Margin No. 3 is more 
delinite, however, for it is marked by an unusually developed 
"• special area" in the Pecatonica esker belt, and by an impor- 
tant one in the Cedarville belt. These are practically the 
western termini proper of their respective belts, and indicate 
the institution of vigorous melting and large subglacial 
streams. While the ice-sheet was wasting away from the 
country west of this line, the climate was still moderately se- 
vere and melting was at a minimum. But from the time 
when the ice-front passed the line indicated by margin No. 3, 
it was subject to rapid destruction. Between the two esker 
belts, margin No. 3 is further defined by a thickening of the 
till, which is sometimes massed into a low, smooth, moraine- 
like ridge. A boulder belt also appears at intervals along 
this line. It apparently bounds the loess deposit of Lake 
Lena, with its accompanying black soil, on their eastern side; 
and the main deposition of the silt is considered to have been 
contemporaneous with the sub-stage of the ice-sheet during 
which its front coincided with margin No. 3. If we may 
judge from present evidence, the ice-front remained longer on 
this line than at the outer drift margin. It was, also, a mure 
important sub-stage* than any which followed. 
Margin No. 4 is indicated by a "special area" in the Ce- 
darville belt, which apparently corresponds to one in the Pee- 
*Tiie term sub-stdr/c is used in this paper as a synonym of the mo- 
raine-forming subdivisions of the grand stages or epochs of glaciation, 
such as that which formed the Wisconsin drift-sheet. 
