We also encounter, in the southern provinces of America, in the midst of the copper-coloured races of whom I have already spoken, a group of Indians, almost black, whom Prichard, the illustrious ethnologist, has designated the _Mediterranean_, and whose features recall in a striking manner those of some of the Californian tribes. Is this resemblance a sign of the close relationship existing between two peoples placed, as it were, at the two extremities of the world? We can hardly admit the supposition. It seems more probable that it results from the analogy of the climates, and perhaps still more surely from that of the soils, which appear to exercise a mysterious but a powerful influence upon the modification of species and races. [Illustration] BOOK V. _THE POLAR DESERTS--THE MOUNTAINS._ CHAPTER I. THE POLAR DESERTS. In countries which enjoy an always elevated temperature, the excess of their fertility is not much more favourable than extreme dryness to the material and moral development of man. There can be no doubt that the exuberant vegetation is a potent cause of the insalubrity of the atmosphere. And thus it comes that civilization, commerce, industry, labour, have only been able to establish themselves and to make any considerable progress in temperate or even cold countries, where man has found a climate more healthy, but at the same time sufficiently unequal, and often sufficiently inclement, to compel him to defend himself by various means against the rigour of the atmosphere, and a soil capable of furnishing him abundantly with the products necessary for his wants, but on the condition that he gains them by intelligent and persistent toil--by the "sweat of his brow."