40 INDIAN FOREST MEMOIRS. 



Fernandez remarks : — 



" This absence of water at the surface is characteristic of all the streams of the 

 Dun, and is due to the great depth of the loose mass of boulders and shingle 

 into which the water sinks, to reappear only where the underlying imperme- 

 able band of clay comes up near the surface. Thus even the Suswa and the 

 Song rivers become dry for several miles of their intermediate course." 1 



These streams become mountain torrents in the rainy season, quickly rising and falling 

 after heavy rain, and then bring down masses of boulders, shingle and sand which they 

 deposit as they flow along. 



These streams also continually change their course and, leaving behind their former 

 alluvial deposits to gradually become covered with vegetation, proceed to erode new chan- 

 nels and form fresh deposits elsewhere, in the course of which areas often carrying valu- 

 able forest may be entirely swept away and fertile fields overwhelmed with boulders and 

 sand. 



This continual denudation and deposition is more or less characteristic of the entire 

 Sub-Himalayan tract which contains some of the most valuable Indian Sal forests, and in 

 the locality now dealt with, omitting the dry wind-swept higher slopes and ridges of the 

 Siwalik range which carry comparatively valueless stunted forest, three main types of 

 topography, each of which is capable of supporting a distinct type of vegetation, can be 

 more or less clearly distinguished as below : — 



I. Areas where the soil, at least during some months of the year, tends to become 

 more or less water-logged and which in their extreme development become 

 perennially wet swamps. The soil as a rule contains a considerable propor- 

 tion of clay. 

 II. The dry alluvial deposits of sand, gravel and boulders chiefly found in and near 

 the stream beds, where the water table is usually at. a considerable depth 

 below the surface. These possess little power of retaining water or of rais- 

 ing the subsoil water by capillarity to replace that lost at the surface by 

 evaporation. They are liable to be excessively heated by solar radiation in 

 the day and in the hot season and to be excessively cooled by terrestrial radia- 

 tion at night and in the winter, especially where the free circulation of air is 

 impeded. 

 III. Areas where the soil is characterised by containing a considerable admixture of 

 clay, or humus, or both, and which varies from light to fairly stiff loam. 

 These areas are to a considerable extent confined to the higher plateaus owing 

 partly to the stiff soil offering resistance to erosion. They are as a rule well 

 drained anc: the soil therefore retains water well, while the water lost at the 



1 I.e., p. 4. 



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