PHYSICAL FEATURES, 1 87 



Section 2. — Hydrography. 



All this region is an area of closed drainage, and, as is usual in 

 regions where the rainfall is of the scantiest, the hydrographic basins 

 are very irregularly and vaguely defined. Very little water ever 

 reaches the great lake basins or " hamuns," most of which are now 

 barren plains of sun -cracked alluvium. The absence of rain has not 

 allowed the formation of any well-marked river-course possessing an 

 individuality of its own. Where the mountain ranges overlook the 

 desert plain, innumerable dry channels follow the slopes parallel to 

 one another. They never contain any water except for a few hours at 

 a time in the rare event of a shower of rain ; not one of them con- 

 tains a stream running even for part of a season, such as would 

 excavate its bed more deeply and gradually draw towards it as tribu- 

 taries the supply of the neighbouring channels. Each of these 

 furrows runs from the hill into the plain, following an almost straight 

 course absolutely independently from its neighbours. I have observed 

 instances in which two such channels excavated to widely different 

 depths approach so close to one another for a certain part of their 

 course, that they are separated by nothing but a mere ridge. Yet 

 even the shallower of the two is excavated sufficiently deep to show 

 that it has already existed for a lengthy period along the same course 

 which it now occupies. In a country favoured by a normal and 

 regularly distributed amount of rainfall, the ravine flowing at a higher 

 level would have been diverted from its course to become a tributary 

 of the adjacent deeper channel long before it had become so deeply 

 intrenched within its own banks. After a course of five or six miles, or 

 often much less, these parallel ravines become completely obliter- 

 ated in the great desert plain. The topography thus produced is 

 most typically represented on map 89, north of Nushki. 



Where the ranges are perhaps favoured with a little more rain- 

 fall, instead of being merely furrowed along their slopes by the 

 channels above described, they are cut through at intervals by deeper 

 channels which occasionally form narrow gorges or rifts locally called 



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