August, 1955 



EvERs: Hill- Prairies of Illinois 



373 



are found along the east blutts 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 \alley changes from a 

 northwest-southeast trend to one that is 

 north-south or northeast-southwest, as in 



In Illinois, soils derived from loess sup- 

 port both plairie 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 h\ ice during the Tazewell sub- 



Fig. 3. — Calcareous concretions or "loess kindchen" from Phegley hill prairie near Prairie 

 du Rocher, Randolph Coum}'. Such concretions are common on many prairie slopes in Illinois. 



Carroll, ]\Iadison, 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 1. Loess on the bluff's in 

 many places is somewh-Tt 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 AVisconsin glaciation, fig. 4. 

 Soils derived from till support both prai- 

 rie and forest in Illinois. 



Exposure. — Hill prairies are most 

 abundant on the northeast sides of the 

 valle\s, fig. 1, where the bluffs trend 

 northwest-southeast, or on bluff's that bor- 

 der the wide, flat bottomlands or broad, 

 flat terraces over which winds blow with 

 little hindrance, or on bluff's that are high. 

 Certain physiographic situations, direc- 

 tion and steepness of slopes, altitudes of 

 bluffs, and width of adjacent bottomlands 

 are \erv ad\antageous 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 



