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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 A'ariatiou in plant societies which grow in soils having the same 

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

 intimately as.'^ociaied witJi the physiography of a region and as the topog- 

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

 modilied. 



Physiography. 



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

 lake which at consecutive periotLs has occupied three distinct levels. 



The First I.ake. — A level plain whose elevation is about eight feet 

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

 marshy outlet to the Tipiiecanoo Rivir. Below the outlet two moraines 

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

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

 moraines were continuous immediately after the glacial recession, while 

 the Tippecanoe drainage liasiu was being established. This woiild have 

 caused a large irregulaz' area, including the area descril)id. to ))e luidi-r 

 water. 



The Second Lake. — When these larger muiaines were cut in two tliis 

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

 nearly parallel to the Tippecanoe Kiver. Tlie outline of this lake can be 

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

 gi-ow in what was tlie shallower part of it. 



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

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

 around the margin tended to liring the lake lioor 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 i-egion occupied by the present swamp. 



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

 the outlet of the lake at higher levels, but through a channel r,^^o. miie in 

 length, whose slope was very slight. 



V>y a seiies of excavations on the west side of the swani'i it A^\>s 

 determined tliat the slope of the sand imdei' the peat for the 1' .■i-rbl'- 

 two feet, beginning at the peat margin A\'as one in ten; that i.' 



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