;94 
IOWA ACADEMY OF SCIENCE Vol. XXIV, 1917 
which is bare of trees, and carries only prairie plants. The 
variety of plant habitats to be fonnd in close proximity to each 
other here varies from high, dry, exposed prairie, through 
scrubby bur oak woods, to heavy forest, as one descends the north 
face of the bluff. The bluffs along the river have deep ravines 
running back several hundred yards to the south in various 
places, and at certain points in these, small bogs appear about 
springs, while high, bare-topped ridges separate them. Photo- 
graphs of the bluff from various points of view are given in 
Plates XI and XII. The profile of the hill is shown in figure 80. 
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StatioYvJl 
If ft ajkn> 4 , AJsmfu. 
‘/-OO ft. S. AasiMA, 
8 ft A 
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Figure 80 
This region has been worked over by the glaciers several times. 
Bed rock outcrops a few miles to the north, where ledges of 
the well-known Sioux quartzite appear along the river, and 
about a mile northeast of the area studied, on the north side of 
ihe river, are ledges of Cretaceous rock. Over the wooded bluffs 
we have a thin humus which becomes thicker in the wooded 
areas, and on the river bottom. Beneath the humus on the bluffs 
is a moderate amount of wind-blown loess, in no case observed 
to be more than four feet thick. Below this is a very extensive 
bed of yellow Kansan drift, at Syverud Bluff not less than sixty 
feet in thickness. Next below this come several feet of water 
bearing Aftonian gravels of an interglacial period, and then 
come great deposits of the earliest glacial drift that covered 
