793 Lieut. Irwin's Memoir of Afghanistan. [Oct. 



cannot thus decide without adverting to other circumstances. If the 

 low hills be. extensive, the flood they occasion may surpass that arising 

 from the melting of the high snows, under which are situated the up- 

 permost sources of the river. If the river be highest in summer, we 

 may decide that it has lofty mountains at its head. This conclusion 

 however is just only when we put out of view the periods of the 

 rains, and decide from those of the thaws only. Both considerations 

 must be combined in our judgment in particular instances, to which 

 we now proceed. 



80. The periods of the Indus and the rivers of the Punjab are nearly 

 the same as those of the Ganges and its tributary branches, which are 

 lowest in the winter, rise somewhat in the spring, and are highest in 

 the middle of August. The rise in the great Ganges is perhaps gra- 

 dual, certain, and nearly of the same quantity in different years ; for 

 being fed by many streams one chance and anomoly corrects another, 

 but the same is not true of its branches, including the upper Ganges 

 itself. The annual rise at Hurdwar is six or seven feet; in the lower 

 part of Bengal above the influence of the tide, it is thirty-one. This 

 difference, may I believe, be shewn to be a consequence from the ge- 

 neral principles of hydrostatics ; it must therefore be supposed to exist 

 in the case of the Indus and its branches, for they also run in a 

 champaign country and yielding soil. My inquiries tend to confirm 

 this opinion. After rains of uncommon severity the rivers of the 

 Punjab sometimes rise to a great height ; the effect however is tem- 

 porary, and many seasons pass in which no such extraordinary floods 

 occur. The great Indus after the junction of the Punjnud is from 

 various causes less affected by local and temporary circumstances, but 

 its regular and annual rise is greater than that of any of its branches. 

 The branches have diversities among themselves not reducible under 

 one general rule, but caused by special circumstances. The Ranee, 

 which is the least of all the rivers, had yet in 1809 a rise equal to any 

 of them. When other circumstances are the same, streams which run 

 in sand increase more in breadth in their flood season, and those 

 which run in clay increase more in depth. The annual rise of the 

 great Indus I reckon about sixteen feet; that of the Ganges is thirty- 

 one ; and of the Nile twenty-four. The proportion in which their waters 

 are respectively increased it would be more difficult to estimate. The 

 same causes combine in the raising the Indus and its branches, and 

 the rivers of our provinces — that it both thaws and rains. The effects 

 in this respect are different, in that there is no inundation in the Pun- 

 jab or Sindh, for we cannot apply that term where the tracts covered 



