BIG SPRING PRAIRIE. 45. 



seemingly contradictory plant societies. Upon closer 

 examination, it was ascertained that, although the sur- 

 face level of the muck differed but moderately, the drift 

 clay beneath is not nearly so uniform in level. Conse- 

 quently, while at some places the clay bed lies one or 

 two feet beneath the surface, at others it lies at a depth 

 unknown at present. On account of the dip of the rock 

 strata of the ridges adjacent to the prairie, the lower 

 strata of muck are surcharged with water, which pre- 

 vents excavating a hole deep enough to determine depth 

 of muck. A long iron pipe or wooden pole might be 

 driven into the muck, but it would be impossible to de- 

 termine, whether the entire distance of easy penetra- 

 tion were muck, quick sand, or a plastic mixture of 

 sand and clay. For a conservative estimate we may 

 state that the muck in some portions is at least eight 

 or ten feet deep. As there is this difierence in the na- 

 ture and depth of the soil and sub-soil, and as in the 

 neighborhood of the old lake remnant the soil is more 

 sandy than elsewhere, and as the plant societies vary 

 according to these factors, we shall deal jointly of the 

 nature of the soil in the various portions and the charac- 

 teristic plant societies thereon. 



The first division of plant societies on Big Springs 

 Prairie would be the wooded portions, and the Prairie 

 proper. The wooded portions may be classified under 

 the following divisions : 



1 The Sand Dune Forest. 



2 The Outcrop Forest. 



3 The Clay Island Forest. 



4 The Clay Bank Forest. 



5 The Burned Area Thicket. 



These divisions will be more fully treated of in the 

 division of Forest Encroachment or Introduction upon 

 Prairie, the Order and Cause. 



The prairie proper supports various plant societies 

 according to its elevation, proximity to ditches, and ef- 



