191 1] STEVENSON— FORMATION OF COAL BEDS. 525 



because of climatic conditions, but it suffices to protect these soils 

 on all except the steepest slopes. Limestone soils, occupying much 

 of the area, are very apt to " wash " when under cultivation, but 

 where covered with forest even the steepest slopes retain their cover 

 of humus and the run-off water is never turbid. Sandstone soils 

 vary much in resistance, when bared, but where they are protected 

 by a thin cover of humus the waste is insignificant. The water of 

 small streams flowing from forest mountain-sheds is clear and pure. 

 The great resistance offered by humus is apparent from the figures 

 given by Ashe. Pines growing on poor soils, rarely yield more than 

 2 inches ; yet this protects all except the steepest slopes. Chestnut 

 oak and white oak give but 3 inches ; they too grow on poor soils, 

 which, when exposed, are torn away rapidly. Other woods give 

 from 5 to 6 inches of litter, which is so absorbent that for several 

 days after a rain one can squeeze water from it as from a sponge. 

 Ashe's observations show that this vegetable litter, in the semi- 

 decomposed condition, is so interwoven that it not only protects the 

 underlying soil but also itself resists removal as does a well-rooted 

 sod. The streams coming from the humus covered area are free 

 from vegetable matter, aside from occasional twigs and, at times, 

 some soluble matters leached from the humus. 



The White mountains of New Hampshire illustrate well the 

 incompetence of rainfall to remove living vegetation. The rock in 

 that region is mostly granite and the soil, formed since the glacial 

 period, is very largely humus. The slopes are abrupt and the walls 

 of gorges frequently show more than 50 degrees ; but most of the 

 area below timber line has a dense cover of vegetation, largely spruce. 

 Yet rains have always been frequent and many times almost deluge- 

 like. The covering of humus is undisturbed by those rains ; even 

 wiiere lumbermen have cut away the forest and left their litter and 

 the humus exposed to the fury of storms, one finds little evidence 

 of removal. 



Cloudbursts or extraordinary downpours of rain have occurred 

 many times within this area. C. H. Hitchcock has described the 

 flood in the Flume at Franconia, which washed away the great 

 boulder which had been dropped by the retreating ice and had re- 



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