206 The American Geologist. March, i8s>7 
several of the most prominent areas consist almost exclusive- 
ly of (ine sand, and, although they have been deeply eroded, 
they still retain their prominence over neighboring portions of 
the belt. Post-Kansan erosion (chiefly Aftonian) has removed 
a large part of the deposits, and to it is due mainly the pres- 
ent topography of the belts. The higher knolls are those por- 
tions which, being capped with coarse gravel, were less deeply 
eroded. The original topography can sometimes be restored 
by studying the internal structure. The ridges thus become 
s.noother and more regular, but the sj>ecial areas are not oblit- 
erated. In short, after a careful study of the region, no doubt 
can remain that originally the belts of stratified drift ridges 
and knolls had these points of special development. 
The Manner of Deposition op thp: Stkatifiei> Dkift. 
When the "iceberg" theory was favorably received to ex- 
plain the glacial phenomena of North America, the range of 
gravel hills in the Leaf river valley was attributed to the ac- 
tion of marine currents in the sea, which was supposed to 
have covered the entire glaciated area. Later, when the gla- 
cial-deposits were recognized to be due to the action of land 
ice, and after the sig-nificance of the terminal moraines had 
been determined, this range of hills, probably because of its 
being at right angles to the glacial border, was classed with 
medial moraines. Daring the past ten years, however, its true 
nature has been generally recognized, namely, that it is the 
deposit of a stream which flowed on, through or under the 
ice, and which had a course at right angles to the border of 
the ice-sheet or approximately parallel with the direction of 
ice-movement; in short, that it belongs to the class of glacial 
drift deposits included under the term eskers. I shall assume, 
as needing no demonstration, (1) that the stratified gravel 
and sand of the Pecatonica and Leaf river basins owe their 
existence to a series of streams which resulted from the melt- 
ing of the border portions of the ice-sheet; and (2) that 
these streams had walls or banks of iee. the deposits being 
laid down mainly within the margin of the glacier. It will 
be interesting, however, to discuss some of the minor particu- 
lars, such as (a) whether these streams flowed in channels, 
melted into the ice, or in tunnels; (b) whether the deposits- 
were laid down at the mouths of the streams or along their 
