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| Keywords: The Quarterly journal of the Geological Society of London (12645922603).jpg 1863 <br> FERGUSSOX DELTA OP THE GAXGF S <br> 32 <br> they leave their beds and consequently force them to deposit their <br> silt in their immediate proximity <br> The first consequence of this is that water resists water far better <br> than earth does A river can attack its banks in detail can eat <br> them away bit by bit and carry off the spoil ; but the still water <br> seizing the silt forces the river to deposit it exactly where it is most <br> useful in forming a barrier against further incursions and so finally <br> repels its advance <br> In India these backwaters are called j heels and are large sheets <br> of clear water existing during the cold weather at about the same <br> level as the river During the rains they rise nearly pari passu with <br> the rivers partly owing to the quantity of rain-water that drains <br> into them partly to leakage through sandy strata partly to small <br> creeks or openings from the rivers and partly also from almost all of <br> them being open at their lower ends so as to feel the reflex of the <br> inundation From all these causes when the river is at such a <br> height as to overtop its banks it meets this body of still water <br> fig 1 and not being able to set it in motion it deposits its silt in <br> the limit between the moving and the still bodies Even when the <br> jheel has not risen so fast as the river a few days' overflow serves <br> to restore the equilibrium and then the deposition goes on as before <br> In most parts of Bengal indigo -planters and others avail them- <br> selves of this interval to cut canals or khals through the banks in <br> order that the river-water may flow into the jheels and so raise their <br> beds and render them fit for cultivation Even under the most <br> favourable circumstances however the action seldom extends more <br> than 100 or 200 yards from the banks ; and when the equilibrium of <br> water is restored the silt is deposited in the canal which requires <br> consequently to be cleared out every year and after a few years <br> the deposit beyond has raised itself to the height of the bank so <br> that further progress in that direction is impossible and the opening <br> in the bank of the river is then soon completely obliterated <br> Fig 1 ” Diagram-section across the Bed of a River <br> Clear water <br> – w '35 Water <br> 5 a containing <br> p sediment River-Water <br> Clear water <br> Silt forming the bed of the River <br> It is extremely difficult to fix the exact point at which this deposit <br> begins to take place ; but as far as I have hitherto been able to ascer- <br> tain rivers flowing through a country whose slope is more than 6 <br> inches in a mile have rather a tendency to deepen their channels <br> and abrade their banks and the land in their immediate proximity <br> is lower than at a little distance At 3 inches in the mile or <br> The fell of the Indus from Attoek to the sea being on an average 1 foot per <br> VOL XIX PART I Z 35328296 109632 51125 Page 325 Text v 19 http //www biodiversitylibrary org/page/35328296 1863 Geological Society of London Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 19 1863 Geology Periodicals Smithsonian Libraries bhl page 35328296 dc identifier http //biodiversitylibrary org/page/35328296 smithsonian libraries Information field Flickr posted date ISOdate 2014-02-20 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12645922603 2015-08-27 11 52 41 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1863 Photos uploaded from Flickr by Fæ using a script | ||||
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