IV. Were natural obstacles indeed insurmountable to nations destitute of our perfected means of locomotion? This question must be considered from two points of view, as the migrations in question are by land or sea. The former demands but little attention. The weakness of man, and the strength of the barriers which the accidents of land, vegetation, or fauna might oppose to him, have unquestionably been much exaggerated. Man has always been able to vanquish ferocious animals, the rhinoceros having formed part of his food as early as the Quaternary period. His course has never been arrested by mountains, even when encumbered by everything which could make the passage most difficult. Hannibal crossed the Alps with his elephants, and Bonaparte with artillery. The progress of the Asiatic hordes was no more stopped by the Palus Meotides than that of Fernand de Soto by the marshes of Florida. Deserts are daily traversed by caravans; and as to rivers, there is not a savage who does not know how to cross them upon some raft or other. The truth, as is too well proved by the history of travel, is, that man alone stops man. Where the latter did not exist, there was nothing to oppose the progress of tribes or nations advancing slowly and at their own leisure, outstripping or passing each other in turn, establishing secondary centres, from which, after a time, fresh migrations would take place. Even in an inhabited country, a superior invading race would not act otherwise. It was thus that the Aryans conquered India, that the Paouians advanced, who, starting from a centre still unknown, arrived at the Gaboon with a line of front of about 250 miles. V. I might dwell upon these general considerations, but it will be better to recall briefly a fact which, though of recent date, is too generally forgotten, and which shows how an entire population can effect a great migration although they meet with obstacles of every kind over a great tract of country.