10 BIG SPRING PRAIRIE. 



Along the summits and edges of the ridges, the soiU 

 varying from dark red clay to lighter shades, is exceed- 

 ingly thin, the fields being covered with angular stones. 



In the shallow natural drainage courses, the soil is 

 a rich loam, as it is also on the fiat median plain of 

 West Ridge. Along the base the soil is frequently 

 quite sandy. 



Whereas the greatest heights of both North and 

 West Ridge are about one hundred and fifty feet each, 

 and the median plains of same about thirty to fifty feet 

 higher than prairie, the country to the north and west 

 of the prairie is as a rule, only about three to six feet 

 higher than the level along edge of prarie. Even this 

 elevation is a gradual slope reaching this height at a 

 distance of forty to eighty rods from the edge of prairie. 

 Although this slope is so very gradual, only in a few lo- 

 calities is there a gradual transition from forest to prai- 

 rie. For the greater portion of its extent, the line of 

 demarkation between forest and prairie is quite dis- 

 tinct. Bordering upon the southwestern portion of the 

 prairie, there is a low wet woods in which there is no 

 perceptible difference in level between it and the ad- 

 joining prairie. 



Characteristic Vegetation of the Ridges. 



For the sake of more clearly indicating the nature 

 of the various plant societies in a more or less limited 

 area, it will be found expedient to employ five classes 

 of plant societies instead of the three given by Warm- 

 ing. The classes under this scheme would be : 



(1) Xerophytic area. 



(2) Xero-mesophytic area. 



(3) Mesophytic area. 



(4) Hydromesophytic area. 



(5) Hydrophytic area. 



The first, third, and fifth conform to Warming's 

 classes. 



