546 
scoparius, and the probable extent of mixed associations. In the Andro- 
pogon furcatus prairies remaining in morainal depressions and the small 
areas in the vicinity of Chicago coarse herbs occur only as scattered 
individuals, as in the Southern Illinoisan glaciation. The older writers 
speak of these prairies as a “sea of grasses”, and it is probable that 
coarse herbs did not occupy very large areas, as their presence would 
certainly have called forth exclamations from the men of those days. 
Wherever the prairie grasses have been greatly disturbed along railway 
rights-of-way, both north and south, these coarse herbs become conspicu- 
ous, and this has probably led many to ascribe to them more prominence 
than they deserve. Gerhard and others report them as being abundant 
on hillsides and near forest borders, and they may have been rather 
prominent on the shallow soils of morainal ridges. 
The xerophytic grass association dominated by Andropogon scoparius 
is the characteristic association of these shallow soils. Relic patches 
of this grass are most frequently found on the broken topography near 
woodlands where the subsoil has been exposed by erosion. As in the 
southern part of the state, Sorghastrum nutans, Sporobolus heterolepis, 
and coarse herbs are also more conspicuous in these areas. Vestal (28) 
finds that this association is not very extensively developed in the upper 
Wisconsin glaciation. The data obtaimed in this survey agree with his 
statement. 
The available data bearing upon the extent of mixed associations 
in this region are rather insufficient for quantitative estimates. In the 
Southern Ilinoisan glaciation mixed associations were of minor impor- 
tance as most of that region had reached the climax stage of development 
and was dominated by but one species, Andropogon furcatus. It is 
probable that mixed associations representing a transition stage in suc- 
cession to this climax from the drier uplands may have been more ex- 
tensive on the younger topography of the Wisconsin glaciation, but 
conclusive evidence is wanting. 
From my records it appears evident that under the most favorable 
natural conditions the dominant species shown in the previous diagrams 
of this report must have occurred in almost pure stands; that coarse 
herbs were not abundant except on eroding soils and near forest borders; 
and that mixed associations were limited largely to transition zones. 
This conclusion was corroborated by every early settler with whom I 
talked and also by Dr. John H. Schaffner (22), who lived on the 
Andropogon prairies in Kansas and had many opportunities to see them 
in their natural conditions. They all report that in the best growing 
seasons Andropogon furcatus grew so tall that a man sitting on a horse 
could not see over it, and that the location of cattle and horses could 
frequently not be determined except by the waving of the tall grass as 
they passed through it. This height together with its production of a 
close sod and dense vegetative growth was sufficient to exclude most 
of the other prairie plants. Dr. Schaffner also reports that Andropogon 
Scoparius generally occurred in very pure stands, and that coarse herbs 
