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Show 25 8 GULF STREAM. . d erally only three feet deep, of water, ten miles broad,da~ gent rs driven to one side, and · d ha Its wa e . has, by a strong wm ' . .1! t deep while the wmdward . d to become six 1ee ' h sustame so as A t there£ore he observes, w en l 'd d * s wa er, ' side was at th tr yi t ·c annot escape, acquires a h.i gher level, so, pent up so a . the same operatiOn produces a . l here tt can escape' l d' m a p ace w . nt will extend to a greater or ess IS-current; and this curre £ b which it is produced. The tance, according to the dorce . yed of all currents, is the gulf · d best etermm most extensive an d . tropical regions; and, after h. 1 ts westwar m stream, w 1c 1 se d H e where it runs nearly at the doubling the Cape of G~o l' opco' nsiderably to the northward, f il an hour, memes 1 . rate o two m es f Af . then crosses the At antic, 1 t n coast o rica, along t l~ wes er d in the Gulf of Mexico, passes out at and, ha~mg accumulate with a velocity of four miles an hour, the Stratts of Bahama, . 'I s until the stream has prowhich is not reduced to t~~ ;nne hundred miles in the direcc. eeded to the distanc~ ~~:~; ~he:t island it meets with a current twn of Newfoundlan . ffi ' B on the coast of Greenland, setting southward from Ba n ds tahy, ast One branch extends b d fl t d towar s e e · and is th~re ~ e e~·~ ther runs towards the north; so that in that directlon, w I e anoh d f America and theW est . I d ood t e pro uce o . d frmts, Pants, an w ' h f Ireland the Hebrides, an Indies, are drifted to the s ores o ' even to Spitzbergen. . ffi ts of tides and currents, it In describing the destr?ymg e ecd t 'I because we have not will be necessary to ent~r mto so:eof ~h~ deltas of many rivers, the advantage here, as m the ca h' h h s resulted from the conof viewing the aggregate mass w lC a ~enturies, at certain tinual transportation of matter' for manyt f accumulation as points. We must infer the greatda~~~: r~movinO' force; and a corollary from th~ proofs adduce . o th whole. ogreater than this it will not be difficult to show Is, on e . that of running water on the land. hares of the British If we follow the eastern and ~outhernl sd t the Land's End Ul · Th Je m Shet an , o · l'slands from our tlma· u . f changes smce in Corn' wall, we shall fin d evl· d e~ce off a1 s enke' s do and degree of the historical era, very illustrative od t Je Il.ndcration. In this force exerted by t h e agen t s now un. t cr fc otnras cing the power of survey we shall have an opp?rtu~I y oand estuaries; on bold, the sea on islands, promontories, ays, "' Rennel on the Channel-current. ROCK-MASSES DRIFTED BY THE SEA. 259 lofty cliffs as well as on low shores ; and on every description of rock and soil, from granite to blown sand. We shall afterwards explain by reference to other regions, some phenomena of which our own coast furnishes no examples. Shetland Islands.-The northernmost group of the British islands, the Shetland, are composed of a great variety of primary and trap rocks, including granite, gneiss, mica-slate, serpentine, greenstone, and many others, with some secondary rocks, chiefly sandstone and conglomerate. These isles are exposed continually to the uncontrol1ed violence of the Atlantic, for no land intervenes between their western shores and America. The prevalence, therefore, of strong westerly gales, causes the waves to be sometimes driven with irresistible force upon the coast, while there is also a current setting from the north. The spray of the sea aids the decomposition of the rocks, and prepares them to be breached by the mechanical force of the waves. Steep cliffs are hollowed out into deep caves and lofty arches; and almost every promontory ends in a cluster of rocks, imitating the forms of columns, pinnacles, and obelisks. Modern observations show that the reduction of continuous tracts to such insular masses is a process in which Nature is still actively engaged. " The Isle of Stenness," says Dr. Hibbert, " presents a scene of unequalled desolation. In stormy winters, huge blocks of stones are overturned, or are removed from their native beds, and hurried up a slight acclivity to a distance almost incredible. In the winter of 180.2, a tabular-shaped mass, eight feet two inches by seven feet, and five feet one inch thick, was dislodged from its bed, and removed to a distance of from eighty to ninety feet. I measured the recent bed from which a block had been carried away the preceding winter (A. D. 1818), and found it to be seventeen feet and a half by seven feet, and the depth two feet eight inches. The removed mass had been borne to a distance of thirty feet, when it was shivered into thirteen or more lesser fragments, some of which were carried still farther, from thirty to one hundred and twenty feet. A block, nine feet two inches by six feet and a half, and four feet thick, was hurried up the acclivity to a distance of one hundred and fifty feet*." • Dr. Hibbert, Description of the Shetland Islands, p. 527. Edin., 1822. S2 |