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Show CHAPTER XIV. , 1 D lt of the Ganges an d D ur rampooter-lts size, rate of advance, Occamc de tas- 0 f. ad 't Format '1 011 an d destruction of islands-Abundance and nah1re o 1ts 0 P 091 . s- D lt f the Mississippi-Deposits of drift wood d'l 1 dahons- e a 0 of croco 1 es-. nun f t'h e Ye ll ow S ea-Rennell's estimate of the mud car- -Gradual fillmg up 0 . f valleys illustrated by the growth b tl G nges-Formahon o ried down GYr le a . eral-Convergence of deltas-Con· n ing of new strata m gen . ogfl odmeletraast-es-Vo aPri ous causes of straf 1fi ca f 10 n-Direction oflammro-Remarks on the interchange of land and sea. OCEANIC DELTAS. . . of deltas are those in which rivers, on THE remammg class d t the influence o'f the tides. In · tl sea are expose o . d entermg 1e ' h that an estuary Is produce , or this case it frequently bappents d by Renne11 where, instead . d l . it has een erme ' negative e ta, as f the land upon the sea, the ocean enters of any encroachment o d t ates into the land beyond the the river's m~uth, an h:r:n;h~s happens, the tides and cur-general coast-lme. 'yY . t ' 1· n tl1e distribution of trans- 1 d mmatmg acren s . rents are t le pre o l o a tl1erefore of such estuanes, d. t 'l'he p 1enomen , ' po. rted se Imedn ·. our exam.m at ' n ,,vhen we treat of the move- 10 • will come un et 1 tl1c volume of fresh-water f l But w 1enever f ments o t 1e ocean. d lmost neutralize the force o . t counteract an a 1 1~ so great a~ o . all cases where the latter agents lave tides and currents, and m d' tancc the whole of the ffi . to remove to a Js . d 1 not su 1Cient power ] b rivers oceamc etas sediment periodically brough\ c ~wnow ~elect a' few illustrative are produced. Of these, we s la n examples. Gancres and the Durrampooter Della of the Ganges.-The . o . the world into a gulf descend fl'Om t l1 e h1.g 1 l es t mountams m ·1 · ' . t 1to the contmen · ' d d d t renty-five ml CS 11 which runs two hun re an " 1 'ver of the two, but The Burrampooter I.S somew h a t the arcbrhe r n .. ed by a sma 11 er f tl MeO'na w en JOin • it first takes the name o 1e b ' h' ain on its umon stream so cal led ' and afterwards loses t IS ag D1nTA OF THE OANCES, 241 with the Ganges, at the distance of about forty miles from the sea. The area of the delta of the Ganges (without including that of the Burrampooter, which has now become conterminous) is considerably more than double that of the Nile; and its head commences at a distance of two hundred and twenty miles, in a direct line fl'Om the sea. That part of the delta bordering on the sea is composed of a labyrinth of rivers and creeks, all of which m·e salt, except those immediately communicating with the 'principal arm of the Ganges. '!'his tract, known by the name of the Woods, or Sunderbunds, a wilderness infested by tigers and alligators, is, according to Rennell, equal in extent to the whole principality of Wales*. The base of this magnificent delta is two hundred miles in length, including the space occupied by the two great arms of the Ganges which bound it on either side. On the sea-coast there are eight great openings, each of which has evidently, at some ancient periods, served in its turn as the principal channel of discharge. Although the flux and reflux of the tide extend even to the head of the delta, when the river is low, yet, when it is periodically swollen by tropical rains, the velocity of the stream counteracts the tidal current, so that, except very neat· the sea, the ebb and flow become insensible. During· the flood-season, therefore, the Ganges almost assumes the character of a rivet· entering a lake or inland sea; the movements of the ocean being then subordinate to the force of the river, and only slightly disturbing its operations. The great gain of the delta in height and area takes place during the inundations; and during other seasons of the year, the ocean makes reprisals, scouring out the channels, and sometimes devouring rich alluvial plains. So great is the quantity of mud and sand poured by the Ganges into the gulf in the flood-season, that the sea only recovers its transparency at the distance of sixty miles from the coast. 'l'he general slope, therefore, of the new strata must be extremely gradual. ]~y the charts recently published, it appears that there is a gt·adual deepening from four to about sixty fathoms, as we proceed from the base of the delta to the distance of about one hundred miles into the Bay of Bengal. At some few points seventy, or even one hundred fathoms are obtained at that * Account of the Ganges and Burramr,ooter Rivers, by Major Rennell, Phil. Trans, 1781. ~l R |