WATER CIRCULATION AND ITS CONTROL 



345 



banks of sward or above the stone wall 

 are carefully leveled and the water 

 which falls upon them is retained. 

 Agriculture is thus extended not only 

 over far-spreading plains and lowlands, 

 Init up the steep banks of river gorges 

 and ravines. The famous vineyards of 

 the Rhine are planted on rock wall ter- 

 races, on steep slopes such as we aban- 

 don to erosion. As our population in- 

 creases and the demand for agricultural 

 land becomes more urgent we, too, will 

 build terraces, and high river banks 

 throughout the hnmid regions will 

 grow special products. Land hunger 

 will eventually force us to it — not soon, 

 however — and in the meantime our 

 steep, cleared lands cannot be left a 

 prey to erosion. They must be recov- 

 ered where gullied and must be pro- 

 tected from gullying by watchful care, 

 such as that which guards Holland 

 from the sea. Our enemy is no less 

 dangerous, not a whit less insidious and 

 persistent. Since terracing is a possi- 

 bility of the future only, we must re- 

 store the forest trees. They have held 

 the soil during ages and on them we 

 can confidently rely. 



We are wont to think that reforesta- 

 tion is a need of high mountains only, 

 but the need is not thus limited. Tt ex- 



tends to all steep cleared slopes. Thou- 

 sands of miles of these stretch along 

 our rivers, from Georgia to Maine, 

 from Mississippi to Minnesota. 

 Throughout the humid region they bor- 

 der every river. Along all their length, 

 in all their ramifications that penetrate 

 the richest agricultural districts, they 

 must necessarily be covered by trees. 



From the plains and gentle slopes ap- 

 propriate to farming there rise in all 

 hill and mountain districts steeper 

 slopes that are not api)ropriate to farm- 

 ing. When farmed thev are quickly 

 erode 1 and destroyed. It may be set 

 down as an obvious economic principle 

 that no land is appropriate to a use 

 which destroys its usefulness. This 

 principle is net affected by the fact that 

 ignorant persons clear and cultivate 

 such land extensively. In the southern 

 Appalachian Mountains it is commonly 

 but five years from virgin forest to 

 abandoned fields. The mountain slopes' 

 are not agricultural lands. Themselves 

 destroyed by erosion, they damage 

 other lands and the water courses below 

 them. When that damage is assessable 

 by law upon the ignorance that causes 

 it, agriculture* will be restricted to ap- 

 propriate fields. 



f To be concluded ) 



Salt Fiver Dam Site, Arizona 



