IOWA. ACADEMY OP SCIENCES. 
i ( 
of the river, there being no borings that extended to the rock 
bottom. A few years later a boring at Mont Clare, Iowa, was 
sunk in the old valley and brought confirmation to General 
Warren’s interpretation.* The accompanying sketch map, 
figure 2, sets forth the position of the old valley and its rela- 
tion to the one across the rapids. 
Figure 1. Sketch map of regloa discussed, showing course of old channels. 
Note of Explanation.— The abandoned portion of the pre-glacial channel of the 
Mississippi is shaded. Hachures are used to Indicate valley borders both below and 
above high terraces and along the temporary Mississippi channel, opened at the 
Illinoian stage of glaciation. The extent of the high terrace in Missouri has not been 
determined. 
It should not be inferred that this broad, preglacial valley 
was necessarily a line of discharge for the whole of the pres- 
ent drainage basin of the upper Mississippi. The available 
evidence concerning the preglacial drainage, though imper- 
fect, is thought to indicate that a large part of the region 
•■^Buried River Channels in Southwestern Iowa, by 0. H. Cordon, Iowa Geol. Surv. 
Report for 1S93. pp. 236-255. Figs. 5, 6 and 7. Published in 1895 as Vol. Ill of the present 
survey 
