'911 J STEVEXSOX— FORMATION OF COAL BEDS. 527 



mountains, cut by canyon-like gorges, to broad river valleys with 

 wide bottoms in which the streams meander. This study concerns 

 also some matters to be considered hereafter, but they are included 

 here for convenience of reference. 



Glenn asserts that, in forested areas, erosion is at its minimum, 

 for the soil is protected by the litter from impact of raindrops. As 

 drops move down the slope, they are checked by the litter or are 

 absorbed by it, and the rainfall moves so slowly through the mass 

 that for hours after rainfall, the cover is full of water. Even such 

 gullies as were seen have their bottoms covered with litter and 

 plants, showing that the erosion, by which they have been produced, 

 is very slow. Streams flowing from the forested regions rise grad- 

 ually during heavy rains and fall to normal more gradually, because 

 the litter retards flow. Such streams, even when highest, are, as a 

 rule, but slightly discolored and that discoloration is caused in great 

 part by macerated fragments of leaves and decaying plants, for they 

 carry little mineral matter in suspension. Some of them remain 

 wholly clear even when swollen to far beyond their normal stage. 

 But removal of the forest brings about an abrupt change. The pro- 

 tective efficiency of even a root-matted soil is evident, for when a 

 tree is uprooted or a road is cut, so as to break the continuity, erosion 

 begins at once. The contrast between forested and denuded areas 

 is so striking that no argument is needed. Grass-covered slopes may 

 be destroyed by breaks made when a cow crosses them after pro- 

 longed rainfall, but erosion can be checked by covering the surface 

 with litter, held in place by brush ; weeds and bushes spring up 

 quickly. The writer adds his testimony in confirmation of these 

 observations by Glenn, for he has seen many thousands of acres of 

 cleared land, which had been abandoned after a few years of culti- 

 vation and which now are covered by a dense growth of hard wood — 

 and this on the steep slopes of the Mrginian Appalachians. 



Glenn's volume is a commentary on the protective influence of 

 vegetation and on its resistance to erosion. The changes in the rivers 

 since the removal of forests from their headwaters, the increased 

 erosion, the increased destructiveness of floods owing to the greate*- 

 load of inorganic matter are set forth clearly on almost every page. 



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