96 BIG SPRING PRAIRIE- 



depth of muck is decreased to such an extent that roots 

 of trees can penetrate to a firmer stratum. 



10 Trees require a firm support for their roots. - 

 Consequently, successful tree growth can not occur 

 where muck is deep and loose. 



11. Order of tree encroachment upon prairie was 

 as follows: 



(a) On limestone island, 



(b) On sand dunes or beaches, 



(c) On clay islands or clay banks. 



(d) Along drainage ditches. 



(e) On severely burned areas. 



12, Portions of this prairie were formerly wooded, 

 as is evident from the buried forests. Forests probably 

 destroyed by flooding on account of construction of 

 beaver-dams. 



13, The highest portions of natural prairie possess 

 the most distinctive marsh characters. 



14. Parallel ditches at intervals of four rods 

 needed to drain this area properly for the successful 

 cultivation of the best paying crops. 



