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Show CHAPTER XV. t' effects of ti.d es an d cu rrents-Shifting of .t heir posi- Destroying and transpor mg t' _, Causes of currents-Achon of the . 1 · of the lues-tion- Diffcrences m t 10 nsc . 1 1 1 Large blocks removed-Effllcts Shetland s anc s-sea on the British coast- . f hyry-Isles reduced to clusters l d m a mass o porp of lightning-Breac l cause t f Scotland-Stones thrown up on the I 1 East coas o of rocks-Orkney s cs- W t . f the cliffs of Holderness, Nor-t f England- as e o Bell Rock-East coas o . -Origin of submarine forests- s'lf up of estuar1cs folk and Suffolk- 1 wg . t - S ffulk coast-Dunwich-Essex ' Submanne fores s u . Yarmouth estuary- . S d -Coast of Kent-Formation Tl mes-Gooclwm an s . . coast-Estuary of the la C t of Dorset-Portland-OrJgm or Coast of Hunts- oas of Straits of Dover- . . tradition-Coast of Brittany. the Chese1 B ank -Cornwall-Llonnesse t of great bodies of water, termed ALTHOUGH the movem~n s 1 lue to very distinct causes, re m genera ( b tides and currents, a . Jr rately for they produce, y 'd their euects sepa • ' . 1 we cannot consl er l . 11 are sub1ects of geologiCa their . th se chanO'es w nc J 'd d J. oint actiOn, o . o .r ns we before consl ere W view these lOrces • l 1'd inquiry. e may ed in destroying portions of t le .s? 1 rivers first, as employ . tllem to other localities; ' 1· nd removmCT · · 1 Crust of the eart 1, a tC: t Some of the prmcipa secondly, as repro d uc t'I V e of new s• 1 a ao. f the globe depen d on . l . larCTe rerrwns 't currents whlc 1 traverse otol . . tation of the earth on I s . I d these on Je IO permanent wmc s~ ~n . d to the sun :-they are causes, axis, and its positwn m l~ega~des themselves, and, like them, therefore, as constant as ue :dental circumstances, but on depend on n~ tempor~ry o:e~c~~e motions of the. heave?ly the laws whiCh preside o f their influence m altermg b od 1. es. But ' although thh e sum boe very cons t an t throughout the surface of the eat·t rna~ 'h these operations are successi.v e epoc1 1 S, ye t the pomthsi fwt peerrep etually. 'I' Il e h e·io cr ht displayed in the ful~cst energy s ·iolence and velocity of c~r· to which the tides nse, and the ~ n the actual configuratiOn rents, depend in a great measL~·~i:e of continental or insular of the land, the contour o! ~ lo~1o hannels the peculiar f?rm of coast, the depth and ~rea t 1~d ~1; a co:nbination of cll'cumd the bottom of seas-m a wo ' . lly by many igneous an stances which are rna d e t o v ary contmua RISE OF •.tun TIDES. 257 aqueous causes, and, among the rest, by tides and currents • .Although these agents, therefore, of decay and reproduction, are local in reference to periods of short duration, such as those which history in general embraces, they arc nevertheless universal, if we extend our views to a sufficient lapse of ages. The tides, as is well known, rise in certain channels, bays, and estuaries, to an elevation far above the average height of the same tides in more open parts of the coast, or on islands in the main ocean. In all lakes, and in most inland seas, the tides are not perceptible. In the Mediterranean, even, deep and extensive as is that sea, they are only sensible in certain localities, and they then rarely rise more than six inches above the mean level. In the Straits of Messina, however, there is an ebb and flow every six hours, to the amount of two feet, but this elevation is partly due to the peculiar set of the currents. In islands remote from the shore, the rise of the tides is slight, as at St. Helena, for example, where it rarely exceeds three feet,·~.:. In the estuary of the Severn, the rise at King's Road near Bristol is forty-two feet; and at Chepstow on the Wye, a small river which opens into the same estuary, about fifty feet. All the intermediate elevations may be found at different places on our coast. Thus, at Milford Haven, the rise is thirty-six feet ; at London, and the promontory of Beachy Head, eighteen feet ; at the Needles, in the Isle of Wight, nine feet; at Weymouth, seven; at Lowestoff about five; at Great Yarmouth, still less . That movements of no inconsiderable magnitude should be impressed on an expansive ocean, by winds blowing for many months in one direction, may easily be conceived, when we observe the effects produced in our own seas by the temporary action of the same cause. It is well known that a strong southwest or north-west wind, invariably raises the tides to an unusual height along the east coast of England, and in the Channel; and that a north-west wind of any continuance causes the Baltic to rise two feet and upwards above its ordinary level. Smeaton ascertained, by experiment, that in a canal four miles in length, the water was kept up four inches l1igher at one end than at the other, merely Ly the action of the wind along the canal ; and Renncl informs us, that a large piece , ~ Romme, Vents et Courans, vol. ii.1 Sc1., March, 1829, p. 2. Rev. F. Fallows, Quart. Journ. of Vot, I. s |