185 



CHAPTER IX. 



Rio Plata — Flocks of butterflies — Beetles alive in tlie sea — Aeronaut 

 spiders — Pelagic animals — Phosphorescence of sea — Port Desire — 

 Spanish settlements — Zoology — Guanaco — Excursion to head of har- 

 bour — Indian grave — Port St. Julian — Geology of Patagonia, succes- 

 sive terraces, transport of pebbles —Fossil gigantic llama — Types of 

 organization constant — Change in zoology of America — Causes of 

 extinction. 



PATAGONIA. 



December Gth^ 1833. — The Beagle sailed from the Rio 

 Plata, never again to enter its muddy stream. Our course 

 was directed to Port Desire, on the coast of Patagonia. 

 Before proceeding any further, I will here put together a 

 few observations made at sea. 



Several times when the ship has been some mUes off the 

 mouth of the Plata, and at other times when off the shores 

 of Northern Patagonia, we have been surrounded by in- 

 sects. One evening, when we were about ten miles 

 from the Bay of San Bias, vast numbers of butterflies, 

 in bands or flocks of countless mjTiads, extended as far 

 as the eye could range. Even by the aid of a glass it 

 was not possible to see a space free from butterflies. The 

 seamen cried out ** it was snowing butterflies," and such in 

 fact was the appearance. More species than one were pre- 

 sent, but the main part belonged to a kind very similar to, 

 but not identical with, the common Enghsh Colias edusa.* 

 Some moths and hymenoptera accompanied the butterflies ; 

 and a fine Calosoma flew on board. Other instances are 

 known of this beetle having been caught far out at sea ; and 

 this is the more remarkable, as the greater number of the 

 Carabidee seldom or never take wing. The day had been 



* I am indebted to Mr. Waterhouse for naming these and other 

 insects. 



