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proof is required how fmall the proportion of velocity is, that the descent communicates. It is then, to the impetus originating at the spring head, or at the place where adventitious waters are poured in, and fucceffively communicated to every part of the stream, that we are principally to attribute the velocity, which is greater or leffer, according to the quantity of water poured in. f

*

In common, there is found on one fide of the river an almost perpendicular bank, more or less elevated above the stream, according to the season, and with deep water near it: and on the oppofite fide a bank, shelving away fo gradually as to occafion fhallow water. at some distance from the margin. This is more particularly; the case in the most winding parts of the river, because the very opěrat tion of winding produces the steep and shelving banks*: for the current is always ftrongest on the external fide of the curve formed. by the serpentine course of the river; and its continual action on the banks either undermines them †, or washes them down. In places where the current is remarkably rapid, or the foil uncommonly loofe, fuch tracts of land are swept away in the course of one seafon, as would astonish those who have not been eye-witnesses to the magnitude and force of the mighty ftreams occafioned by the periodical rains of the tropical regions. This neceffarily produces a gradual change in the course of the river; what is loft on one fide being gained on the other, by the mere operation of the ftream: for the fallen pieces of the bank diffolve quickly into muddy fand, which is hurried away by the current along the border of the channel, to the point from whence the river turns off to form the next reach

Hence it is, that the fection of a river, that winds through a loose foil, approaches nearly to an obtufe angled-triangle, one of whofe fides is exceedingly fhort and difproportioned to the other two But when a river perfeveres in a straight course, the fection becomes

nearly the half of an ellipfis divided longitudinally. See Plate I.

3.

+ In the dry season fome of thefe banks are more than 30 feet high, and often fall down inpieces of many tons weight, and occasion so sudden and violent an agitation of the water, as fometimes to fink large boats that happen to be near the fhore.

where

where the ftream growing weak, it finds a refting place: and helps to form a fhelving bank, which commences at the point, and extends downwards, along the fide of the fucceeding reach.

by the last steep bank

To account for the flackness of the current at the point, it is neceffary to obferve, that the ftrongest part of it, inftead of turning. short round the point, preferves for some time the direction given it and is accordingly thrown obliquely across the bed of the river to the bay on the oppofite fide, and purfues its courfe along it, till the intervention of another point again obliges. it to change fides. See plate I.

In those few parts of the river that are ftraight, the banks undergo the least alteration *, as the current runs parallel to them; but the leaft inflection of course, has the effect of throwing the current against the bank; and if this happens in a part where the foil is compofed of loose fand, it produces in time a ferpentine winding.

It is evident, that the repeated additions made to the fhelving bank before mentioned, become in time an encroachment on the channel of the river; and this is again counter-balanced by the depredations made on the opposite steep bank, the fragments of which either bring about a repetition of the circumftances above recited, or form a bank or shallow in the midst of the channel. Thus a steep and a shelving bank are alternately formed in the crooked parts of the river (the steep one being the indented fide, and the shelving one the projecting); and thus, a continual fluctuation of courfe is induced in all the winding parts of the river; each meander having a perpetual tendency to deviate more and more from the line of the general course of the river, by eating deeper into the bays, and at the fame time adding to the points; till either the opposite bays

It is more than probable, that the ftraight parts owe their existence to the tenacity of the foil of which their banks are compofed. Whatever the caufe may be, the effect very clearly points out fuch fituations as the propereft for placing towns in.

meet,

meet, or the stream breaks through the narrow isthmus, and reftores a temporary straightness to the channel.

Several of the windings of the Ganges and its branches are faft approaching to this state; and in others, it actually exists at present. The experience of these changes fhould operate against attempting canals of any length, in the higher parts of the country; and:I much doubt, if any in the lower parts would long continue navigable. During eleven years of my refidence in Bengal, the outlet or head of the Jellinghy river was gradually removed three quarters of a mile farther down and by two furveys of a part of the adjacent bank of the Ganges, taken about the distance of nine years from each other, it appeared that the breadth of an English mile and a half had been taken away. This is, however, the moft rapid change that I have noticed; a mile in ten or twelve years being the usual rate of incroachment, in places where the current ftrikes with the greatest force; namely, where two adjoining reaches approach nearest to a right angle. In fuch fituations it not unfrequently excavates gulfs of confiderable length within the bank. These gulfs are in the direction of the strongest parts of the ftream; and are, in fact, the young shoots (if I may fo express myself) which in time ftrike out and become branches of the river: for we gene rally find them at thofe turnings that have the fmalleft angles t., :

Two causes, widely different from each other, occafion the meandering courses of rivers; the one, the irregularity of the ground through which they run, which obliges them to wander in quest of a declivity the other, the loofenefs of the foil, which yields

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The Count DE BUFFON advifes the digging of such gulfs in the banks of ordinary ri vers, with a view to divert the current, when bridges or other buildings are endangered by it. + The courses of thefe branches at the efflux, generally, if not always, become retrograde to the courfe of the river; for, a fand bank accumulating at the upper point of feparation, gives an oblique direction upwards, to the ftream, which would otherwife run out at right angles. This fand bank being always on the increase, occafions a corrofion of the oppofite bank; and by this means all, or moft of the outlets, have a progreffive motion downwards; as I have before remarked of the Jellingly river, in the foregoing page.

to

to the friction of the border of the ftream. The meanders in the first case, are, of course, as digreffive and irregular as the furface they are projected on: but, in the latter, they are fo far reducible to rule, that rivers of unequal bulk will, under fimilar circumstances, take a circuit to wind in, whofe extent is in proportion to their respective breadths: for I have obferved, that when a branchi of the Ganges is fallen fo low as to occupy only a part of its bed, it no longer continues in the line of its old courfe; but works itself a new channel, which winds from fide to fide acrofs the former one. I have obferved too, that in two ftreams, of equal fize, that which has the floweft current has alfo the finalleft windings: for as thefe (in the prefent cafe) are folely owing to the depredations made on the banks, by the force of the current; fo the extent of thefe de predations, or, in other words, the dimenfions of the windings, will be determined by the degree of force acting on the banks.

The windings of the Ganges in the plains, are, doubtless, owing to the looseness of the foil: and (I think) the proof of it is, that they are perpetually changing; which thofe, originally induced by an inequality of furface, can feldom, or never do *.

I can easily suppose, that if the Ganges was turned into a straight canal, cut through the ground it now traverses in the most winding parts of its course, its ftraightnefs would be of fhort duration: Some yielding part of the bank, or that which happened to be the most strongly acted on, would first be corroded or dissolved: thus a bay or cavity would be formed in the fide of the bank. begets an inflection of the current, which, falling obliquely on the fide of the bay, corrodes it inceffantly. When the current has paffed the innermoft part of the bay, it receives a new direction, and

This

• It has been remarked, that the courfes of rivers become more winding as they approach the fea. This, I believe, will only hold good in fuch as take the latter part of their course through a fandy foil. In the Ganges, and other rivers fubject to confiderable variations in the bulk of their streams, the best marks of the vicinity of the fea, are, the lowness of the river banks, and the increasing muddinefs of the fhallows in its bed.

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is

is thrown obliquely towards the oppofite fide of the canal, depofiting in its way the matter excavated from the bay, and which begins to form a shallow or bank contiguous to the border of the canal. Here then is the origin of fuch windings as owe their existence to the nature of the foil. The bay, fo corroded, in time becomes large enough to give a new direction to the body of the canal: and the matter excavated from the bay, is fo difpofed as to affift in throwing the current against the opposite bank; where a process, fimilar to that I have been defcribing, will be begun.

The action of the current on the bank will alfo have the effect of deepening the border of the channel near it; and this again increases the velocity of the current in that part. Thus would the canal gradually take a new form, till it became what the river now is. Even when the windings have leffened the defcent one half, we still find the current too powerful for the banks to withstand it.

There are not wanting inftances of a total change of courfe in fome of the Bengal' rivers *. The Cofa river (equal to the Rhine) once ran by Purneah, and joined the Ganges oppofite Rajemal. Its junction is now 45 miles higher up. Gour, the ancient capital of Bengal, ftood on the old bank of the Ganges: although its ruins. are 4 or 5 miles from the present bank.

Appearances favour very strongly the opinion, that the Ganges had its former bed in the tract now occupied by the lakes and moraffes between Nattore and Jaffiergunge, ftriking out of its prefent courfe at Bauleah, and paffing by Pootyah. With an equal degree of probability (favoured by tradition) we may trace its fuppofed courfe by Dacca, to a junction with the Burrampooter or Megna near Fringybazar; where the accumulation of two fuch mighty ftreams, probably scooped out the prefent amazing bed of the MEGNA. See plate II.

* The Mootyjy! lake is one of the windings of a former channel of the Coffimbuzar river. Megna and Burrampoater are names belonging to the fame river in different parts of its courfe. The Megna falls into the Burrampooter; and, though a much finaller river, communicates its name to the other during the rest of its course.

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