172 ARE SOILS ENEICHED, IMPOVERISHED, pt. hi. 



The beautiful artificial terracing of the hill-side, 

 which we see in southern mountain cultivation, origi- 

 nates in the necessity of catching the stream of soil 

 from above, and preventing its farther descent to the 

 valley below, down which it would be washed, whether 

 it were a dry valley or a river valley. 



In unusually heavy rains numbers of these terrace 

 walls give way ; and when a terrace goes which is high 

 up the hill-side, a sort of earthen avalanche takes place, 

 bearing crops, soil, and stone walls in succession to the 

 vale below. 



In these works man shows himself as a strong con- 

 servative. In alluding to a man as a leveller^ our great 

 geologist admirably remarks : ' By ploughing up thou- 

 sands of square miles, and exposing a surface for part 

 of the year to the action of the elements, we assist the 

 abrading force of rain, aud diminish the conservative 

 effects of vegetation ; ' and by fencing these thousands 

 of square miles, man acts as a very universal conser- 

 vative. 



The existence of upper valleys, or dry rivers of 

 soil, proves that, were there no such things as rivers on 

 the globe, the scooping power of rain would still give 

 the same alternation of hills with valleys sloping to the 

 sea which now obtains, and the same waste and de- 

 nudation from lateral wash would still take place. The 

 river only makes its own channel (which is much en- 

 larged by rain floods), and in that channel assists in 

 conveying away the denudation brought to it by rain, 



