20 The American Geologist. Jannary, 1895 
country to the east, from which it is absent. This differ- 
ence along the border is so great that no differential subsi- 
dence theory will explain it. To suppose that the ice ad- 
vanced and plowed it up and removed it from the country 
where no loess is now found, is equally preposterous, for 
there certainly is no remnant of such a loess mantle anj'- 
where under the newer drift sheet, nor are the slight morainic 
ridges which bound it at all comparable in size with those 
that would have been produced by the plowing up of a loess 
deposit, a portion of which must have escaped being carried 
away by subglacial and extraglacial drainage. 
Sequence op the Glacial History. 
The sequence of events here during the Ice age, as indicated 
by these observations, may be summarized as follows : 
1. Northwestern Illinois, after having passed through one 
period of glaciation, had a prolonged period of subaerial ero- 
sion and soil formation, during which the climatal conditions 
were probably similar to what they are to-day. Near the end 
of this period, but while the surface was still covered with its 
temperate vegetation and the streams full of invertebrate ani- 
mals, we find the land in process of subsidence. The return- 
ing ice had certainly not yet reached the mouth of the Peca- 
tonica river, and perhaps was many miles away ; but the 
streams had begun to silt up their valleys, forming low and 
gravelly flood-plains. 
2. Next we find the ice moving up the Pecatonica valle}^ 
the land going down towards sea level and the water level 
rising, producing long lake-like rivers through which the gla- 
cier- born currents rushed, carrying coarse sediment. The 
climate had grown cold, and the former flora and fauna had 
hirgely disappeared. 
3. Still the subsidence continues; the lakes rise, and finer 
sediment is carried. The ice advance has, in the Pecatonica 
valley at least, reached its climax; and the front remains sta- 
tionary, or nearly so, while the Valley loess is being deposited. 
4. The epeirogenic movement has now reached its culmina- 
tion; nearly the entire region, so far as not covered bj^ the 
mer de glace, is submerged, and the Upland loess is laid down. 
The ice on the eastern side begins to retreat, and for a while 
the loess-depositing waters follow it up. But an elevatoiy 
