VIE IV OF THE PAMPAS 349 



I obtained thirteen species on the shores of the Atlantic, and 

 five on the Pacific, and not one of them is identical. We must 

 except all those species which habitually or occasionally frequent 

 elevated mountains ; and certain birds, which range as far south 

 as the Strait of Magellan. This fact is in perfect accordance 

 with the geological history of the Andes ; for these mountains 

 have existed as a great barrier, since the present races of 

 animals have appeared ; and therefore, unless we suppose the 

 same species to have been created in two different places, we 

 ought not to expect any closer similarity between the organic 

 beings on the opposite sides of the Andes, than on the opposite 

 shores of the ocean. In both cases we must leave out of the 

 question those kinds which have been able to cross the barrier, 

 whether of solid rock or salt water.^ 



A great number of the plants and animals were absolutely 

 the same as, or most closely allied to, those of Patagonia. We 

 here have the agouti, bizcacha, three species of armadillo, the 

 ostrich, certain kinds of partridges and other birds, none of 

 which are ever seen in Chile, but are the characteristic animals 

 of the desert plains of Patagonia. We have likewise many of 

 the same (to the eyes of a person who is not a botanist) thorny 

 stunted bushes, withered grass, and dwarf plants. Even the 

 black slowly-crawling beetles are closely similar, and some, I 

 believe, on rigorous examination, absolutely identical. It had 

 always been to me a subject of regret that we were unavoidably 

 compelled to give up the ascent of the S. Cruz river before 

 reaching the mountains : I always had a latent hope of meeting 

 with some great change in the features of the country ; but I 

 now feel sure that it would only have been following the plains 

 of Patagonia up a mountainous ascent. 



March 2\th. — Early in the morning I climbed up a moun- 

 tain on one side of the valley, and enjoyed a far-extended view 

 over the Pampas. This was a spectacle to which I had always 

 looked forward with interest, but I was disappointed : at the 

 first glance it much resembled a distant view of the ocean, but 

 in the northern parts many irregularities were soon distinguish- 



' This is merely an illustration of the admirable laws, first laid down by Mr. 

 Lyell, on the geographical distribution of animals, as influenced by geological changes. 

 The whole reasoning, of course, is founded on the assumption of the immutability of 

 species; otherwise the difference in the species in the two regions might be con- 

 sidered as superinduced during a length of time. 



