Leverett.] 
456 
[Jan. 1, 
In defence of the latter theory it is maintained that the forest- 
bed was rapidly formed and covered during the numerous oscilla- 
tory retreats and advances, and the erosion of the so-called older 
drift was effected by glacial floods attending the retreats ; the more 
aged appearance of the drift near its southern margin being ac- 
counted for by its supposed larger derivation from residual ma- 
terial gathered by the glacier as it first pushed across the country. 
Whether the forest-bed was formed rapidly or not ; whether pre- 
glacial leaching or postglacial age was the more important factor 
in the production of the aged appearance of the southern margin 
of the drift ; and how far the great erosion is attributable to glacial 
torrents and how far to smaller streams of longer action ; — are prob- 
lems doubtless possible of solution. Alreadj 7 much has been done 
toward solving them, but much remains to be done before it will 
be definitely known to what extent each theory is applicable. 
I wish to present here a line of evidence in support of the theory 
of two distinct epochs, drawn from studies made under the direc- 
tion of Pres. T. C. Chamberlin, in the eastern part of the Missis- 
sippi basin, — one which I think has not yet received due attention, 
namely, the depth to which the carbonates were leached from the 
drift surface during an epoch of deglaciation in the midst of the 
glacial period. 
There are in Illinois, Indiana and Ohio, a series of about ten 
more or less distinct moraines, all having at surface a fresher drift 
than that lying outside their southern limit. Several of these have 
at some depth a till corresponding in character to, and seemingly 
a continuation of, the outlying drift. The southernmost moraine 
has been traced from southwestern Illinois eastward to the Scioto 
river, its further distribution being as yet undetermined . 1 
The till is soft and fresh in appearance to a depth of at least 
twenty feet in this southernmost of the series, and to a depth of 
one hundred feet or more beneath later moraines in central Illinois 
and Indiana. Below it is a hard, partially cemented till, fre- 
quentl } 7 capped by a dark colored soil a few inches in thickness, 
and oxidized to a depth of several feet. The oxidized portion is 
of a brownish yellow color, differing from the oxidized portion of 
the surface tills of the same region which are yellowish gray. This 
a The following cities are situated near it: in Illinois, Litchfield, Hillsboro’, Pana, 
Shelbyville, Mattoon and Paris; in Indiana, Terre Haute, Rockville, Greencastle, Ed- 
inburgh, Columbus, Greensburg, Connersville and Brookville; in Ohio, Lockland, Leb- 
anon, Hillsboro’, Bainbridge and Chillicothe. 
