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. 



