660 FRANK COLLINS BAKER 
of Illinois, of which there are doubtless many, should be examined 
carefully and their biota compared with the recent biota of the same 
region and with localities within the range of the different species. 
This is especially true as regards deposits of an interglacial 
character. : 
Three new mar! deposits are discussed in the present paper, two 
near Mahomet, on the Sangamon River, and the third on the 
campus of the University of Illinois, in Urbana. 
THE URBANA DEPOSITS 
Excavations for the new greenhouse and for drains in the 
neighborhood show the following superposition of strata (section 
made by Dr. T. E. Savage): 
Section of ditch through old pond 
4. Top soil or black clay without pebbles, grading 
downunto number ssbelownte eee eee 20-24 inches 
3. Clay, dark above, becoming light gray and more 
calcareous below; containing numerous mol- 
HUISKeS eee lan) RCO SOD en aii ECA aan Te 18-20 inches 
2. Marl or limestone composed of more or less com- 
pletely broken shells somewhat consolidated by 
Cementiof{CaCosy tet Sau C nie inert re 8-12 inches 
1. Glacial till, pebbly, gray......... ELA gee ah 6-12 inches 
The depth of the section was about four feet. 
The locality from which these fossils came is in a depression 
northeast of the new greenhouses, near the forest nursery. The 
topography at this place suggests a pond of considerable size and 
the molluscan life indicates quite a depth of water, at least in the 
center of the lake or pond. The glacial till here is the Champaign 
till sheet, and the body of water evidently stood in a kettle hole 
on the northern side of the Champaign moraine, which extends 
northwest and southeast through Champaign and Urbana 
(Leverett, 1899, pl. vi). This till sheet is of early Wisconsin age, 
and the relation of the marl to the till suggests that the pond or 
lake may have been inhabited by the mollusks when the late 
Wisconsin ice was resting at the Valparaiso moraine. The 
cemented character of the marl numbered 2 in the section also 
suggests considerable age. This lake or pond may have drained 
northeastward through the present Salt Fork Valley. 
