200 FOREST PLANTING. 



barriers will resist the current. Arrested at each instant 

 by these obstacles, the water will deposit there, little by 

 little, some stones, gravel and earth, thus establishing 

 terraces upon which we may plant whatever is required 

 after they have been consolidated on their banks with 

 sods. If such works are simultaneously established in 

 the bed of a ravine there cannot occur any dangerous 

 accumulation of the waters, and they will run down the 

 mountains without violence, feeding springs and ferti- 

 lizing the fields in the valleys instead of devastating 

 them. 



C. Artificial Irrigation of Mountains Having Very 

 Dry Surface Soil. 



The system just alluded to is of great importance for 

 mountains which have a poor, dry soil, particularly for 

 such as contain much lime, because these, owing to their 

 enormous capacity of absorbing moisture, are especially 

 inclined to dry up at their surface. If this system be 

 applied on such soils, it enables to introduce an artifi- 

 cial irrigation by which the greatest results may be 

 expected. For the trough-like formations of the moun- 

 tain soil will be converted into reservoirs by construct- 

 ing strong dams across their banks and thus catch 

 up the rain and snow waters. They should have outlets 

 at both ends of the dams from which the water, if 

 wanted, is led off into horizontally-running trenches, 

 over which it will flow slowly and equally, irrigating the 

 area down below. The diagrams (pp.196-7) show how such 

 trenches are built. If there should run off more water 

 than is wanted, the surplus is caught up at a similarly 

 situated lower place, and respectively stored or distrib- 

 uted like that in the higher-lying localities. Treated in 

 this way, whole mountains which would in no otherwise 



