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Show ~96 SUBSIDENCE IN EXCESS IN THE PACIFIC. [Ch. XVIII. A reference to our :first volume' will show that a series of ordinary earthquakes might, in the course of~ f~w centuries, convert such a tract of sea into dry land ; and 1t 1s, therefore, a remarkable circumstance that there should be so immense an area in eastern Oceanica, studded with minute islands, without one single spot where there is a wider extent of land than belongs to such islands as Otaheite, Owhyhee, and ~ few others, which either have been or are still the seats of active volcanos. If an equilibrium only were maintained bet~een t~e upheaving and depressing force of earthquakes, large Islands would vel'y soon be formed in the Pacific ; for, in that case, the growth of limestone, the flowing of lava, and the ejection of volcanic ashes, would combine with the upheaving force to form new land. Suppose the shoal which we have described as six h~ndred miles in length, to sink :fifteen feet, and then to remam unmoved for a thousand years; during that interval the growin()' coral may again approach the surface. Then let the m:ss be re-elevated :fifteen feet, .so. that the original reef is restored to its former position : in · this case the new coral formed since the first subsidence, will constitute an island six hundred miles long. An analqgous result would have occurred if a lava-current fifteen feet thick had overflowed the submerged reef. The absence, therefore, gf more extensive tracts of land in the Pacific seems to show that the amount of subsidence by earthquakes exceeds in that .quarter of the ()'lobe at present the elevation due to the same c;ause. b We mentioned that one of the thirty-two islands examined by our naviO'ators in the late expedition, was raised about eighty feet above the level of the sea *. It is call~d Elizabeth or Henderson's Island, and is five miles in length by one in breadth. It has a flat surface, and on all sides except the north, is bounded by perpendicular cliffs a~out fifty feet high, composed entirely of dead coral, more or less porous, honeycombed at the surface, and hardening into a compact calcarem.ts • According tb some accounts between sixty and seventy feet. Ch. XVIII.] ELIZABETH OR HENDERSON's ISLAND. ~97 mass, which possesses the fracture of secondary limestone, and has a species of millepore interspersed through it. These cliffs are considerably undermined by the action of the waves, No.8. Elizabctl& or Hcndcraon'a 1•/and, No.9. Enlarged vieto of part of Elizabqt/& or 11ondcr1011'1181and. and some of them appear on the eve of precipitating their superincumbent weight into the sea. Those which are less injured in this way present no alternate ridges or indication of the different levels which the sea might have occupied at different periods, but a smooth surface, as if the island, which has probably been raised by volcanic agency, had been forced up by one great subterraneous convulsion *. At the distance of a few hundred yards from this island, no bottom could be gained with two hundred fathoms of line. It will be seen from the annexed sketch, communicated to me by Lieutenant Smyth, of the Blossom, that the trees come down to the beach towards the centre of the isle, a break which at first sight resembles the openings which usually lead into lagoons: but the trees stand on a steep slope and no hollow of an ancient lagoon was perceived. The reader will remark that such a mass of limestone represents exactly those horizontal cappings of calcareous strata which we sometimes :find on hills which have tabular summits. As we have at present no proof that Henderson's Island has been upheaved within the historical period, we deviate somewhat from our plan when we describe it in the present chapter; but, as earthquakes are now felt from time to time in this part of the Pacific, and as indications of very recent changes of level * Beecbey, ib. p. 46, |