213 



The theory of Warming is that all plant societies are determined 

 primarily by the water content of the soil. Cowles accepts the proposition 

 of Warming, but thinks it insufficient because of the fact that there is a 

 wide variation in plant societies which grow in soils having the same 

 water content. His most important conclusion is that plant societies are 

 intimately associated with the physiography of a region and as the topog- 

 raphic forms change from one form to another the plant societies arc also 

 modified. 



Physiography. 



The evidence indicates that this swamp has been a lake or a part of a 

 lake which at consecutive periods has occupied three distinct levels. 



The First Lake. — A level plain Avhose elevation is about eight feet 

 above the level of the swamp extends around the swamp and along its 

 marshy outlet to the Tippecanoe River. Below the outlet two moraines 

 approach the river from each side and show indications of being cut by 

 water at their ends. It seems probable that these and possibly other 

 moraines were continuous immediately after the glacial recession, while 

 the Tippecanoe drainage basin^was being established. This would have 

 caused a large irregular area, including the area described, to be under 

 water. 



The Second Lake. — When these larger moraines were cut in two this 

 lake was lowered to the level of a moraine, extending across its outlet and 

 nearly parallel to the Tippecanoe River. The outline of this lake can be 

 pretty accurately traced by the dark peaty soil and the sedges which still 

 grow in what was the shallower part of it. 



The Third Lake. — The erosion of the outlet tended to lower the water- 

 level of the lake while constant deposition of plants that grew and died 

 around the margin tended to bring the lake floor nearer the surface. 

 These processes eventually resulted in limiting the lake to the much deeper 

 "kettlehole" in the northern part of the area described. The kettlehole 

 is the region occupied by the present swamp. 



The outlet of this lake was not through a narrow moraine, as had been 

 the outlet of the lake at higher levels, but through a channel one mile in 

 length, whose slope was very slight. 



By a series of excavations on the west side of the swamp it was 

 determined that the slope of the sand undei' the peat for the first eighty- 

 two feet, beginning at the peat margin was one in ten; that is, for every 



