88 BIG SPRING PRAIRIE. 



clusively that this area was a lake in past glacial times, 

 and incidentally corroborates the conclusion that it was 

 a preglacial drainage valley, as the rock strata near the 

 western end of prairie are 30 feet beneath the surface. 

 As the surface level is lower here than at the points 

 before mentioned, it is evident that the stream flowed 

 northward and westward. The gravel, sand and marl 

 were deposited when the lake was quite deep, and be- 

 fore the abundant aquatic plant life became established. 

 The position of the clay bed seems to confirm Lesque- 

 reaux's explanation in regard to formation of such strata 

 in ponds and sluggish streams from the remains of 

 chara and allied plants. After bulrushes and cat-tails 

 made their appearance the formation of the muck 

 layer began, After a shallow layer of muck had accu- 

 mulated over the clay bed, the area must have become 

 sufficiently elevated to secure natural drainage enough 

 to enable tree seedlings to make their appearance. 

 The clay subsoil offered a sufficiently firm support 

 for successful tree growth. After the forest became 

 established, it is possible that the natural drainage 

 outlet became obstructed, perhaps by the beaver dam 

 before mentioned. In consequence the forest would 

 be flooded and the trees destroyed. 



Buried forests have also been reported as occur- 

 ing on the Vanlue end of the prairie, and may in the 

 future be found to have existed on other unexplored 

 portions. It is indeed a peculiar area scientifically, as 



it is proving practically to the celery and onion grow- 

 ers. 



THE PRAIRE UNDER CULTIVATION. 



Before the first artificial drainage, the cultivation 

 of any portion of the prairie was impossible. Even 

 after the first artificial drainage, only isolated portions 

 were cultivated Drainage was resorted to chiefly to 

 render the prairie safer for pasturage, as cattle and 

 horses frequently mired in this marsh. 



