543 
glaciation were still dominated by Spartina Michauxiana, Calamagrostis 
canadensis, and Panicum virgatum. Owing to the clean farming methods 
practiced in this part of the state it is now very difficult to estimate 
the percentage of swamp prairie formerly occurring on the present 
well-drained farms. But the postglacial history of this area is still 
clearly written in the soil. The wide extent of the deep black soils points 
to a long postglacial period in which swamps dominated by sedges and 
swamp grasses covered large portions of this glaciation. With the gradual 
filling and drainage of these extensive swamps the more mesophytic 
prairies arose. Soil maps showing the comparative depth of the dark 
humus soil could be used in determining the extent of associations and 
also in the estimation of land values. 
Mr. Wiles estimated that from 70 to 90 per cent. of the area of the 
isolated prairie tracts separated by streams near his home in Vermilion 
county was dominated by an almost pure stand of Andropogon furcatus, 
the remainder by slough grasses, sedges, and rushes. He stated, how- 
ever, that more abundant and extensive sloughs were present in the 
prairie tracts northwest of Vermilion county. Farmers who helped drain 
Douglas county say that the area formerly covered by sloughs and 
shallow lakes greatly exceeded the area of tillable land in that county. 
2. THE XERARCH SUCCESSIONS 
The Succession (a) on Upland Glacial Soils 
The succession of associations leading from swamp to the upland 
prairie was found in every case to terminate in an Andropogon furcatus 
association. This raises the questions of the amount of the upland 
prairie soils dominated by this grass and the nature of the successions 
from the more xerophytic areas on upland glacial soils and sand. 
In this survey emphasis was placed upon the Wisconsin and the 
Lower Illinoisan glaciations. On the former the most typical upland 
prairie soil is a brown silt loam, on the latter it is a gray silt loam poorer 
in organic matter and generally less fertile. Both of these surface soil 
types are underlaid at varying depths with the typical clays of the 
glacial till. Outcrops of these glacial clays are among the most 
xerophytic areas of the prairie. 
Owing to the value of this type of land for agriculture, it is now 
practically all under cultivation. The few small relics of Andropogon 
furcatus prairie in the ‘vicinity of morainal depressions previously dis- 
cussed and similar patches near forest borders constitute the only 
prairie tracts of this type found in the Wisconsin glaciation. On the 
southern Illinoisan glaciation several small tracts varying in size from a 
fraction of an acre to 2 acres were found. - With the exception of the 
exposed clay areas these are all Andropogon furcatus prairies. 
Additional data were obtained from railway rights-of-way, old 
line-fences, and from individuals who had lived on these prairies be- 
