Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.2): between the years 1826 and 1836 : describing their examination of the southern shores of South America, and the Beagles's circumnavigation of the globe

1835. MIGRATION — CURRENTS. 505 far, that is quite clear," when, in simple truth, there is no other animal in the whole creation so easily cavight, so portable, requiring so little food for a long period, and at the same time so likely to have been carried, for food, by the aborigines who probably visited the Galapagos Islands on their balsas,* or in large double canoes, long before Colmnbus saw that twink- ling light, which, to his mind, was as the keystone to an arch. Honest Dampier immediately reverted to the tortoises of the West Indies, and of Madagascar,"!" when he saw those of the Galapagos. He had observed too many varieties caused by climate, soil, food, and habits, to entertain a doubt of their being other than a variety of the tortoise kind. As to the ' guanoes'' they were, to his eye, familiar objects. The currents about these islands are very remarkable, for in addition to their velocity, which is from two to five miles an hour, and usually towards the nortli-west,! there is such a sur- prising difference in the temperature of bodies of water moving within a few miles of each other, that this subject must be reserved for further discussion. On one side of an island (Albemarle Island) we found the temperature of the sea, a foot below the surface, 80°. Faht. ; but at the other side it was less than 60°. In brief, those striking differences may be owing to the cool current which comes from the southward alone the coasts of Peru and Chile, and at the Galapagos encounters a far warmer body of water moving from the bay of Panama, a sort of ' gulf stream." The retentive manner in which such ocean rivers preserve their temperature has been frequently remarked : and must have a great effect upon the climates of countries near whose shores they flow. * I have heard that driftwood, not the growth of these islands, is fre- quently found on the south-east shores. On this subject Colnett says (p. 58), " on several parts of the shore there was driftwood, of a larger size than any of the trees that grow on the island : also bamboos and wild sugar canes, with a few small cocoa nuts at full growth, though not larger than a pigeon's egg." -f Dampier, vol. i. p. 102. X In the twentj'-four hours immediately previous to first making these islands, the Beagle was set fifty miles to the west north-west.