524 T. C. CHAM BERLIN 



America 50 tons, and of Africa 44 tons.'^ Of course the data for 

 Africa, South America, and Asia are particularly imperfect, but 

 probably the general import of the figures is essentially true. 

 We may push the essence of Clarke's interpretation a step farther 

 and point to the general correspondence of these figures with the 

 degrees of surface cultivation that obtain in these continents. 

 These stand in essentially the same order, viz., Europe, Asia, North 

 America, South America, and Africa. Of course other factors than 

 soil cultivation enter into the results, but it is obvious that a much 

 cultivated surface, softened by soil-tilth and left naked in its soft- 

 ened state for at least a portion of the year and perhaps for all the 

 year, will suffer much more rapid denudation, other things being 

 equal, than surfaces that are constantly mantled with vegetation 

 and whose soils are knit into coherence by a mat of roots. The dis- 

 tinction between the resistance to denudation of native surfaces 

 in humid areas under temperate and tropical conditions, on the 

 one hand, and well-cultivated surfaces, on the other, seems to find 

 peculiar exemplification in the data of Dole and Stabler — the best 

 now available from which to draw tentative generalizations for work- 

 ing purposes. The measurements on which their results are based 

 have been made in very recent years, in the main, and represent 

 the rate of denudation incident to the present state of surface cul- 

 ture. Soil wastage is now notably high. The raising of corn, to- 

 bacco, cotton, and potatoes is peculiarly tributary to the leaching 

 and wash of soils. In a somewhat different way, roads are also 

 specially tributary to wash . In very marked contrast to the present 

 state of the surface was its condition just previous to settlement 

 by the whites. The soil of the forested regions was not only pro- 

 tected by a permanent overgrowth of trees and a tangled under- 

 growth of bushes and herbaceous plants and by a mat of leaves, 

 twigs, and fallen timber, but by a network of roots and rootlets 

 which bound the soil together. The flow of surface drainage was 

 delayed and equalized by the one group of agencies while the soil 

 was rendered resistant to the relatively gentle water action thus 

 insured by the other. On the prairies, the dense mat of native 



' F. W. Clarke, "A Preliminary Study of Chemical Denudation," Smith Misc. 

 Coll., LVI, No. 5, (1910), p. 7. 



