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.

(15/5.

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 considered as superinduced during a length of time.) A great number of the plants and animals were absolutely the same as, or most closely allied to, those of Patagonia.