46 BIG SPRING PRAIRIE. 



fects of prairie fires in the past. Furthermore, portions 

 of prairie are still natural meadows; others are under 

 a high degree of cultivation; still others were at one 

 time cultivated, but, for a number of years past, have 

 been used for pasturage again. Thus there is presented 

 a varied array of plant societies according to the fore- 

 going conditions and the problem of their ecology be- 

 comes quite a complex one. 



The prairie societies can be considered under the 

 following divisions: 



1 The Natural Meadow Societies. 



2 The Heath Societies. 



3 The Burned Area Societies. 

 a On severe burns. 



b On repeated slight burns. 



4 MeadowSocieties on areas, formerly cultivated. 



5 The Ditch Societies. 



We shall first treat of the contiguous plant socie- 

 ties of the southern portion of the east arm of prairie, 

 as, on the portion represented on Map II, all of the 

 above prairie societies occur, and also some of the wood- 

 land societies. 



The eastern portion of field "A" is slightly higher 

 than the western, but not more than a foot and a half. 

 Bowlders of various sizes are quite numerous in eastern 

 portion, only a few occurring in western portion. The 

 soil in the eastern portion, as seen along ditches is from 

 one and a half to two feet deep, consisting of three 

 layers, a comparatively thick layer of muck, a medium 

 layer of blue clay, and a thin layer of sand resting upon 

 partially disintegrated native Niagara Limestone. The 

 sand was most likely deposited along the shore of the 

 old lake. About two blocks south of this field, the sand 

 layer is considerably deeper as was observed in water- 

 works trenches, which were in line of the original nat- 

 ural drainage course. How the blue clay came to over- 

 lie the sand layer is an unsolved problem, unless Les- 



