SPECIFIC FOOD IN SOILS FOR PLANTS. 301 



having been to crop a piece of land until completely 

 exhausted, and then leave it to the recuperative ef- 

 forts of nature, while new lands were cleared and 

 put under cultivation. 



In the valuable papers of Dr. Hildreth on the coal 

 region of the West, and in the notes of a Naturalist, 

 both to be found in Silling n's Journal, are notices 

 of large tracts on which nothing but a heavy growth 

 of white oak and its kindred trees are found, and 

 the soil of which is full of pitch-pine knots, scattered 

 in the greatest profusion over large districts, on 

 which a pine-tree has not been seen since the dis 

 covery of the country. The inference is irresistible, 

 that, owing to some unexplained cause, these im- 

 mense forests have perished, and their place has 

 been occupied by the magnificent oak woods that 

 now form so conspicuous a feature of these districts. 

 So plentiful are these pine remains in some places, 

 that the collecting and burning them for tar has been 

 a profitable business. 



That there is the same tendency in cultivated 

 plants to change, or to run out and be succeeded by 

 Others, is well known to every one. Continued care 

 is required to keep meadows that lie long in grass 

 from becoming filled with other and worthless vari- 

 eties ; and reseeding and frequent manurings are 

 necessary to prevent the kinds desired in the soil 

 from running out. So soils on which the same crop 

 is too .frequently raised will show a tendency to 

 throw it off in the inferior value of the crop pro- 

 duced. New-England and Eastern New- York were 

 once the best of wheat-growing districts, but have 

 long since ceased to be such ; and the most moment- 

 ous question that can be asked by the Western 

 farmer is, will that region, now so productive, ex- 

 hibit a similar decline T There can be no reason to 

 doubt that it will, unless an improved and more ra- 

 tional mode of farming be adopted to prevent it. 

 As illustrating the changes that take place in soils 



