CH. Ill 



FIXATION OF UNSTABLE SOILS 297 



boulders passing through gaps in the row next above 

 them, a wall being thus put up immediately below each 

 gap in the upper row. Where the boulders are not 

 heavy and the slope not steep, instead of the upper 

 lines of walls, timber barricades, made of stout logs 

 pegged down across the slope, may be put up. Walls 

 lower down the slope must be of increased strength, so 

 as to be able to stop boulders coming with increasing 

 velocity. Indeed it is not unusual to put up on the 

 lower parts of the slopes, instead of walls, great squared 

 heaps of boulders, sometimes 5 or 6 metres (15 to 

 20 ft.) broad and deep and about 2 metres (6 ft.) 

 high, at places where boulders might come from a 

 height and clear all upper obstacles. In the forests 

 below, the fellings must be made carefully under the 

 selection system, and, instead of felling the trees close 

 to the ground, as ought usually to be done, the stools 

 should be left high, i.e. between 1 and 2 metres 

 (3 to 6 ft.) above the ground. They thus help in check- 

 ing boulders and in reducing the damage done. On 

 very steep slopes they may have to be felled even 

 higher than stated above, for boulders comino; down 

 with a great velocity do not merely roll down the slopes, 

 but come down in great bounds. 



