296 SYLVICULTURE IN THE TROPICS 



PT. IV 



the affluents which it receives, and eventually they may 

 have to attain dimensions which will require considerable 

 engineering skill in their construction. 



The slopes above the stream should also be 

 strengthened by wattle-fences or revetment walls, etc., 

 in the manner described above, and further fixed with 

 natural growth of grass and other herbaceous plants, 

 cuttings, layers, or plants. 



A few more words are necessary about the protection 

 of slopes which, although forest-clad below, are liable 



Fig. 96. 



to be bombarded by rolling stones from above. Here 

 again it is necessary to deal with the evil as near its 

 origin as possible, and before the boulders can obtain 

 such an impetus as to be difficult to check. It is usual 

 to stop these by means of several interrupted lines of 

 dry masonry walls set horizontally across the slopes, these 

 walls being erected on a good foundation, for the receipt 

 of which the hill-side is trenched to a sufficient depth, 

 in order to give more stability to these walls they are 

 made thicker at the base than above, the upper surface 

 of the wall being perpendicular and the lower sloped. 

 The walls should be so constructed that they will stop 



