FORESTRY AND CONSERVATION 327 



derground run-off," and it is clear that the thicker the layer of 

 earth, and the more pervious, the more water it would take up and 

 the longer and steadier it would be giving off this underground 

 water. 



The above statement shows exactly what happens all over the 

 land, and is especially noticeable in the mountains. On the soilless, 

 rocky slopes the water runs off as fast as it falls or the snow melts, 

 but on slopes with deep, pervious soils part of the water is stored 

 and continues to flow for months after the rain or the melting of 

 snow has ceased. 



Returning to the experiment with the layer of earth on the 

 table, we notice that if we sprinkle more briskly, part of the earth 

 is carried away, the layer is eroded, and the storage ground is 

 diminished. If covered by a layer of cotton batting this erosion 

 stops, and in addition we gain another very important point the 

 soil is kept softer, and allows water to soak in more easily than when 

 the cotton is wanting, for then the water "pats" down; it hardens 

 the surface where it does not wash it away. Much the same result 

 might be obtained by sowing grass on the layer of earth, for then 

 the tops of the grass would keep the drops from pounding the 

 earth, form a mechanical obstacle to the surface run-off, and the 

 roots would be an additional help in holding the earth and keeping 

 it from washing away. But the grass is small, its tops are short, 

 open, and close to the ground; its roots are short; it rarely forms a 

 dense sod, and, especially in dry countries, it leaves a large part of 

 the ground without protection. Here, then, the larger, long-lived, 

 deep-rooted trees, with dense, shading crowns high above the ground, 

 give far better and more constant protection against erosion, and are 

 far better able to keep the ground in a pervious condition, since they 

 strew it annually with large quantities of leaves and twigs and pro- 

 vide a network of slowly decaying roots which keep the forest soil 

 mellowed for a foot and more in depth. An upturned hemlock, 

 spruce, etc., will readily illustrate how much of the ground is 

 occupied by the roots of these forest trees. 



The trees, then, are in nature what the cotton is in the experi- 

 ment; they help to keep the soil from being carried away, they 

 keep it soft, and they break the force of the downpouring rain. 



How much additional service trees perform by keeping sun and 

 wind from the ground is well illustrated by the forests of the Lake 

 States and Canada, where thousands of swamps have dried up and 

 hundreds of miles of corduroy road have become useless, not by 

 ditching and draining, but by removing the woods and giving sun 

 and wind access to the soil. 



Though there exists numerous forests in this country where the 

 protective function of the woods is not apparent, in the majority of 

 cases, and in all mountain districts without exception, the forest 

 serves both to supply useful material and to protect and improve the 

 ground, and thereby regulate the surface and underground drain- 

 age. (Y. Book.) 



