1863.] 



FERGUSSOX DELTA OP THE GAXGF.S. 



32: 



they leave their beds, and consequently force them to deposit their 

 silt in their immediate proximity. 



The first consequence of this is, that water resists water far better 

 than earth does. A river can attack its banks in detail, can eat 

 them away bit by bit, and carry off the spoil ; but the still water, 

 seizing the silt, forces the river to deposit it exactly where it is most 

 useful in forming a barrier against further incursions, and so finally 

 repels its advance. 



In India these backwaters are called j heels, and are large sheets 

 of clear water existing during the cold weather at about the same 

 level as the river. During the rains they rise nearly pari passu with 

 the rivers, partly owing to the quantity of rain-water that drains 

 into them, partly to leakage through sandy strata, partly to small 

 creeks or openings from the rivers, and partly also from almost all of 

 them being open at their lower ends, so as to feel the reflex of the 

 inundation. From all these causes, when the river is at such a 

 height as to overtop its banks, it meets this body of still water 

 (fig. 1), and, not being able to set it in motion, it deposits its silt in 

 the limit between the moving and the still bodies. Even when the 

 jheel has not risen so fast as the river, a few days' overflow serves 

 to restore the equilibrium, and then the deposition goes on as before. 

 In most parts of Bengal indigo -planters and others avail them- 

 selves of this interval to cut canals, or khals, through the banks, in 

 order that the river-water may flow into the jheels, and so raise their 

 beds and render them fit for cultivation. Even under the most 

 favourable circumstances, however, the action seldom extends more 

 than 100 or 200 yards from the banks ; and, when the equilibrium of 

 water is restored, the silt is deposited in the canal, which requires 

 consequently to be cleared out every year, and after a few years 

 the deposit beyond has raised itself to the height of the bank, so 

 that further progress in that direction is impossible, and the opening 

 in the bank of the river is then soon completely obliterated. 



Fig. 1. — Diagram-section across the Bed of a River. 



Clear water. 



■w '35 Water 



.5 a, containing 



p,^ sediment. River-Water. 



Clear water. 



Silt forming the bed of the River. 



It is extremely difficult to fix the exact point at which this deposit 

 begins to take place ; but, as far as I have hitherto been able to ascer- 

 tain, rivers flowing through a country whose slope is more than 6 

 inches in a mile have rather a tendency to deepen their channels 

 and abrade their banks, and the land in their immediate proximity 

 is lower than at a little distance*. At 3 inches in the mile, or 



* The fell of the Indus from Attoek to the sea being on an average 1 foot per 

 VOL. XIX. PART I. Z 



