58 
IOWA ACADEMY OF SCIENCES. 
over the ancient marsh; lastly, the mantle of yellow clay on 
which another soil has formed and now bears another growth 
of vegetation. 
Thanks are due to Professor Calvin for kind encouragement 
and for the photographs of the section; to Professor Sardeson, 
of Minneapolis, for helpful suggestions, and to Engineer Wil- 
kins, of the Chicago Great Western railroad, for use of the 
profile map. 
EXPLANATION OF PLATE I. 
Section of Pleistocene deposits as shown in the railway cut at Oelwein. 
1. Thin layer of Iowan drift. Materials unoxidized, and boulders fresh 
and sound. 
2. Kansan drift, oxidized and leached near the top. Many of the 
boulders in an advanced stage of decay. Grades downward into unoxidized 
blue till. 
3. Sand boulders in Kansan drift. Upper ends are included in oxidized 
portion of this drift sheet; lower ends extend down into unoxidized portion. 
4. Lower phase of Kansan drift which here shows physical character- 
istics resembling Number Y. 
5. Thin layer of stratified sand, of Aftonian age, overlying peat. 
6. Peat bed of Aftonian age. 
7. Sub- Aftonian drift. 
EVIDENCE OF A SUB-APTONIAN TILL SHEET IN 
NORTHEASTERN IOWA. 
BY S. W BEYER. 
Until very recently, geologists working in Iowa have been 
content to refer the various boulder clays represented in the 
state to two till sheets, a so called “upper” and “lower,” sep- 
arated in many places by the “forest beds” of McGee, or in 
other localities by gravels, often in conjunction with a vegetal 
horizon, the Aftonian of Chamberlin. 
Early in the present year it was suspected by the assistant 
state geologist of Iowa that the lower till in central Iowa was 
not the equivalent of the lower drift sheet at Afton Junction. 
Later in the season Mr. Bain, in company with Prof. T. C. 
Chamberlin of the University of Chicago, revisited the Afton 
section, and what was at first a suspicion rapidly became a con- 
viction. It was clear that the then recognized lower till of 
central and northeastern Iowa, extending southward into Kansas 
