592 Notes on Geology and Mineralogy of Affghanistan. 



valley of the Helmund, must have been cut through by the 

 retiring waters at the time when the neighbouring moun- 

 tains attained their present elevation, and the drain thus 

 formed has served ever since as the bed of the river, which 

 probably then first had origin. The river although it occa- 

 sionally overflows a portion of the alluvial belt in its bed, 

 never reaches to the old right bank ; and that it exercises 

 little influence on its own modern left bank is proved by 

 the existence of the old fort alluded to by Captain Conolly. 

 I do not think however, that the mere absence of a wall on 

 the river face can furnish any evidence that the Helmund 

 once occupied the whole space between the two forts, for 

 the height and abruptness of the banks themselves furnish 

 a much more efficient defence than the walls above, which 

 are raised in most cases to guard against the attacks of rob- 

 ber horsemen. 



Besides which we require to know how the river could 

 a few years since furnish a body of water four miles in 

 breadth, and from 30 to 40 feet deep; while at present it 

 seldom exceeds 8 or 9 feet in depth, even at the flooding or 

 spring time, when the snows are melting.* 



Still stronger proof however that the river has not changed 

 for many years, is to be gathered from the fact that the 

 ancient town and fortress of Killa Beest remain uninjured 

 on the left bank of the Helmund at its junction with the 

 Argandab. The town has not been inhabited for the last 

 century, and is said to have been flourishing in the time of 

 Nousherwan : it is built upon the conglomerate immediately 

 within the fork formed by the confluence of the two rivers. 

 Between the fortress and the Argandab there is a belt of 

 cultivation, while the Helmund flows immediately beneath 

 the walls of the fortress. Both rivers are therefore seen 

 to hug their left banks, and that they did so before Killa 



* It is not its depth, but its force and rapidity which render it impassable at these 

 times. " 



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