August, 1955 
are found along the east bluffs of the 
Mississippi and Illinois rivers, where, in 
some places, they are more than 300 inches 
in depth. Such thick deposits occur in 
places where the valley changes from a 
northwest-southeast trend to one that is 
north-south or northeast-southwest, as in 
Evers: Hint Prairies oF ILLINOIS 373 
In Illinois, soils derived from loess sup- 
port both prairie and forest. 
The only bluff prairie slopes that are 
mantled by glacial drift and that the 
writer examined for this report are in 
Putnam County. These bluffs were last 
covered by ice during the Tazewell sub- 
Fig. 3.—Calcareous concretions or “loess kindchen” from Phegley hill prairie near Prairie 
du Rocher, Randolph County. Such concretions are common on many prairie slopes in Illinois. 
Carroll, Madison, and Jackson counties. 
Other deposits of great thickness occur 
just east of the wide portions of the main 
valleys, as east of the Illinois River valley 
from Mason County south into Morgan 
County. Away from the main river val- 
leys the loess deposits become progressively 
thinner. Not only do the deposits of loess 
become thinner but also the mean particle 
size decreases with distance from the bluffs 
(Smith 1942). Loess on the bluffs in 
many places is somewhat sandy. 
The hydrogen-ion concentration of 
loess, as determined with a Beckman pH 
meter in samples from 10 hill prairies in 
southern and central Illinois, ranges from 
7.86 to 8.41. All samples, when treated 
with dilute hydrochloric acid, effervesced 
freely, showing the presence of calcium 
carbonate. Calcium carbonate is often 
found in the form of concretions, “‘loess 
kindchen,” fig. 3, on prairie slopes. 
stage of the Wisconsin glaciation, fig. 4. 
Soils derived from till support both prai- 
rie and forest in [linois. 
Exposure.—Hill prairies are most 
abundant on the northeast sides of the 
valleys, fig. 1, where the bluffs trend 
northwest-southeast, or on bluffs that bor- 
der the wide, flat bottomlands or broad, 
flat terraces over which winds blow with 
little hindrance, or on bluffs that are high. 
Certain physiographic situations, direc- 
tion and steepness of slopes, altitudes of 
bluffs, and width of adjacent bottomlands 
are very advantageous in bringing about 
high temperature and low humidity, two 
conditions that favor a high evaporation 
rate, which in turn favors prairie (Shimek 
1911). Southwest- and west-facing bluff 
slopes receive more nearly at right angles 
the rays of the hot afternoon (2 o'clock) 
summer sun than do other slopes. Slopes 
that face these directions are subject to 
