OCR Text |
Show 248 SEDIMENT IN RIVER WATER, were tl'Ue that the Ganges, in the flood-seasor~, contained one part in four of mud, we should then be obhged ~o suppose that there passes down, every four. day~, a. quantity ~f mud equal in volume to the water whiCh IS discharged m the course of twenty-four hours. If .the mud ?e ~ssumed to be equal to one-half the specific gravity of ~ramte .(It would,, however, be more), the weight of matter dally earned do':n m the fl 00 (]-season would be about equal to seventy-four times the weight of th' e Great Pyramid of Egypt*· Ei ven I' f.I t. cou ld be proved that the turbid wa~ers. of the Ganges ~on tam o~e part in a hund1·ed of mud, which IS affirmed to be the c~se m regard to the Rhine, we should be brought to the extra?rdma1·y conclusion, that there passes down, every two days, mto the Day of Bengal, a mass about equal in weight and bulk to the Great Pyramid. . The most voluminous current of lava which has flowed from Etna within historical times, was that of 1669. Ferrara, after correcting Borrelli's estimate, calculated the quantity of cu~ic yards of lava in this current, at one hundred and forty millions. Now this would only equal in bulk one-seventh of the sedimentary matter which is carried down in a single year by the Ganges, assuming the average proportion of mud to 1 w~ter to be no mo1·e than one part in one hundred, so that, a lowmg seven grand eruptions in a century, it would require an hundred Etnas to transfer a mass of lava from the subterranean reO'ions to the surface equal in volume to the mud carried dobw n in the same time' from the Himalaya mountam• s m• to t 11e Bay of Bengal t. As considerable labour has been bestowed # According to Rennell, the Ganges discharges, in the floou-scason, 4~5,000 cubic feet of water per second, which gives, in round numbers, 100,000 cub1c feet of mud per second, which X 86;400, the number of seconds in twenty-four hours, = 8 641100 000 the quantity of cubic feet of mud going down the Ganges per diem'. A' ssum' ing' the specific gravity of mud to be half that of grnm·t e, tl1 e ~a tt er would equal4 320 550 000 feet of granite. Now about twelve and a half cub1c feet of granite wei~h o~e t~n; and it is computed, that the Great Pyramid of Egypt, if it were a solid mass of granite, would weigh about 6,000,000 of tons. t According to Ferrara's calculation, about 140,000,000 of cubic yarus of la~~ were poured from the crater of Etna in 1669. This X 27, will give 3,780,000,~ of cubic feet which would be about one-seventh of the amount of mud camcd down by the G' anges in a year ; for, assuming the average prop~r t'1 0n of mu dtobde. one part in 1\ hundred, this would give on an average 800 CUblC feet per secon 00 · 800 X 311557,600, (the number of seconds in a Julian year,) gives 25,246,080,0 · GROUPING OF STRATA lN DELTAS, 2-!9 in computing the volume of lava-streams in Sicily Campania amI. A uvergne, I. t I.s somewhat extmordinary that so' few obser-' vatiOns have been made on the quantity of matter transported by aqueous agents from one part of the earth to another. It would .certainly n~t be difficult to approximate to the amount o! sediment earned down annually by some of the JarO'est rivers, such as the A~azon, Mississippi, Ganges, and oth~rs, because the earthy partiCles conveyed by them to their deltas are fine, and somewhat uniformly spread throuO'hout the stre d 1 . . 1 m 0 am, an t 1e prmc1pa e ux takes place within a limited period during the season of inundation. ArO'uments have been expended in vain for half a century, i~ conti'OvertinO' the opinio? ~f those who h?agine the agency of running wa~er in the extstmg state of thmgs, even if continued through an indefinite lapse of ages, to b.e insignificant, or at least wholly incompetent to produce considerable inequalities on the earth's surface. Some matter-of-fact data should now be accumulated, and we may. confidently affirm, that when the aggregate amount of so~Id matter transported by rivers in a given numbe. r of c~ntunes fro~ a large continent, shall be reduced to ~nthmehcal computatwn, the result will appear most astonishmg to.tho~e who are. not ~n the habit of reflecting how many of the m1ghttest operations 111 nature are effected insensibly witl _ . d. d ' 1 out ?01se o~ Isor. er. '!he volume of matter carried into the se.a m a. given time bemg once ascertained, every geologist Will admit that the whole, with some slight exceptions, is subtracted fmm valleys, not from the tops of interveninO' ridO' or t he sum~It. s of I1 I' ll s; 1.1 1 other words, that anciento valleoyess have been widened and deepened, or new ones formed to th extent of the space which the new deposits, when consoiidatede would occupy. ' Groupin~ of Strata in Deltas.-The changes which have taken place. m deltas, even since the times of history, may sugg~ st ~an! Important considerations in regard to the manner of distn?utton of sediment in subaqueous deposits. Notwith. stand.mg frequent exceptions arising from the interference of ~~::~ety of cau.ses, there are some general Jaws of arrangement must evidently hold good in almost a11 the lakes and seas now fillin If I k .c g up. a a e, J.Or example, be encircled on |