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Show 192 ATLANTIC OCEAN· Dec. 1833. 1 . my notes that having kept a Medusa of the genus a so 1n ' · h · 1 d D. . ti'll I.t was dead the water in whlC It was pace 1anrea, ' . · h b · ht b ecame l umm. ous · When the waves sc.i ntillate w.1 t ng green sparks, I believe it is generally owmg to mmute crus-tacea. But there can be no doubt that very many other pelagic animals, when alive, are phosphorescent .. On two occasions I have observed the sea lummous at con·- siderable depths beneath the surface. Near the mouth of the Plata some circular and oval patches, from two t~ four yards in diameter, and with defined outlines, shone with a steady, but pale light; while the surrounding water only ~ave out a £l ew spark s. The appearance resembled the reflect10n . of the Or some luminous body ; for the edges were smuous moon, · h' h d from the undulation of the surface. The s~Ip, w. IC rew . thirteen feet water, passed over, without disturbmg, ~hese patches. Therefore we must suppose that some ammals were congregated together at a greater depth than the bottom of the vessel. Near Fernando Noronha the sea gave out light in flashes. The appearance was very similar to that which mi?ht be ~xpectedfrom a large fish moving rapidl! through a l~mmous flmd. To this cause the sailors attributed It; at the time, however, I entertained some doubts, on account of the frequency and rapidity of the flashes. With respect to any general observations, I have already stated that the display ~s very much more common in warm than in cold countnes. I have sometimes imagined that a disturbed electrical condition of the atmosphere was most favourable to its production. Certainly I think the sea is most luminous after ~ fe~ da~s of more calm weather than ordinary, during whiCh time It · has swarmed with various animals. Observing that t~e water charged with gelatinous particles is in an impure stat.e, and that the luminous appearance in all common cases IS produced by the agitation of the fluid in contact with the atmosphere, I have always been inclined to consider t~~t the phosphorescence was the res.ult of the decom~os1t1on of the organic particles, by whiCh process (one 1s tempted Dec. 1833. POR1' DESIRE. 193 almost to call it a kind of respiration) the ocean becomes purified. DECEMBER 23n.-We arrived at Port Desire situated in lat. 47°, on the coast of Patagonia. The creek r:ns for about twenty miles inlan?, wit~ ~n irregular width. The Beagle anchored a few miles w1thm the entrance in front of the ruins of an old Spanish settlement. The same eve~ing I ';ent on. shore. The first landing in any new country Is very mterestmg, and especially when as in ~hi~ ~ase, the whole aspect bears the stamp of a marked and md1V1dual character. At the height of between two and three hundred fe~t, a.bove some masses of porphyry, a wide plain extends, whiCh IS truly characteristic of Patagonia. 'rhe surface is quite level, and is composed of well-rounded shingle mixed with a whitish earth. Here and there scattered tufts of brown wiry grass are supported, and still more rarely some low thorny bushes. The weather is dry and pleasant for the fine blue sky is but seldom obscured. When stand~ ing in the middle of one of these desert plains, the view on one side is generally bounded by the escarpment of another plain, rather higher, but equally level and desolate; and on the other side it becomes indistinct from the tremblinO' mirage which seems to rise from the heated surface. 0 The plains are traversed by many broad, flat-bottomed valleys, and in these the bushes grow rather more abundantly. The present drainage of the country is quite insufficient to excavate such large channels. In some of the valleys ancient stunted trees, growing in the very centre of t~Je dry watercourse, seem as if placed to prove how long a tnne had elapsed, since any flood had passed that way. We have evidence, from shells 1ying on the surface, that the plains of gravel have been elevated within a recent epoch above the level of the sea ; and we must look to that period for the excavation of the valleys by the slowly-retiring waters. From the dryness of the climate, a man m3.y walk for days together Qver these plains without finding a single drop of water. Even at the base of the porphyry hills, there VOL. III. 0 |