IOWA ACADEMY OF SCIENCE 
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main stream. This current scoured out a deep trench close to 
bluffs, but, probably when the floods were declining, it deposited 
some of its load in the preglacial gorge between Sageville and Du- 
buque. After the floods subsided the Little Maquoketa met with 
less resistance in flowing backward along the trench cut by the 
west current than it would have encountered in recovering and 
scouring out its preglacial channel. The great gravel ridge or 
plateau (Fig. 6), fifty feet high, which now separates the reversed 
portion of the Little Maquoketa .valley from the main river, was 
doubtless built up in the slacker water between the two currents. 
For a clear presentation of the relations of the reversed stream to 
its abandoned channel, the small map, figure 7, may be consulted. 
Descriptions of Figures. 
Figure 1. — Bluffs a short distance below Lansing, Iowa, showing vertical 
faces fronting the river, but with side slopes and back slopes old and rounded — 
a combination of young and mature topography. 
