SOIL-DENUDATION. 583 



velocity, and may be assumed to be proportional to the sixth 

 power of the velocity of the stream. 



To cite an example, a formidable landslip occurred on the 

 15th November, 1879, at Vitznau, on Lake Lucerne. Here, 

 at the foot of the Kigi, a mass of earth exceeding 35,000 cubic 

 feet, and covered with trees, fell down the mountain side and 

 filled a depression, burying a chapel under mud to a depth of 

 twenty feet. 



Landslips occur frequently in all mountain chains, and in 

 the Himalayas attain vast proportions ; the Gohna landslip, 

 in 1893, for instance, brought down enormous quantities of 

 rock across a valley, damming up a tributary of the River 

 Ganges. This led to the formation of a lake 10 miles long 

 and 500 feet deep, which eventually burst the dam in. August, 

 1894, causing a flood 30 feet deep to rush down the Ganges 

 valley and flood the town of Hardwar. Owing to the establish- 

 ment of telegraphic communication, and to careful watching 

 at the dam, all the inhabitants of the valley received timely 

 warning of the probable bursting of the dam, and no lives 

 were lost. 



2. Damage done. 



Soil-denudation reduces the forest area, buries plantations 

 and young growth in mud, injures and destroys forest roads 

 and other works, and fills up ditches. Ravines that become 

 constantly enlarged by surface drainage are formed on hill- 

 sides, whilst the beds of watercourses are raised, interrupted 

 and altered, by the material brought down by the water; 

 inundations are thus caused. The amount of damage done 

 increases, the steeper the slope and the more broken its 

 contour, and the looser the soil and the greater the weight 

 of the woody growth. Localities where landslips are likely 

 to occur may be recognised beforehand in wet years by cracks 

 forming in the soil. 



8. Protective Rules. 



The best protective rules to adopt against these dangers are : 



(a) Careful maintenance of a continuous woody growth on 



mountain-peaks, ridges and all dangerous slopes. Forests in 



