In the background of the same sketch we see animals, reduced to the state of domestic cattle, being driven towards the group at work. By this particular feature we have wished to point out that the polished-stone epoch was also that of the domestication of animals, and that even at this early period the sheep, the dog and the horse had been tamed by man, and served him either as auxiliaries or companions. The traces of agriculture which we have remarked on as existing in the caves of Ariége, are also found in other parts of France. Round the hearths in the department of Puy-de-Dôme, M. Pommerol discovered carbonised wheat intermingled with pottery and flint instruments. The men of the period we are now considering no longer devoted themselves exclusively to the pursuits of hunting and fishing. They now began to exercise the noble profession of agriculture, which was destined to be subsequently the chief source of national wealth. _Navigation._--The first origin of the art of navigation must be ascribed to the polished-stone epoch. With regard to this subject, let us pay attention to what is said on the point by M. G. de Mortillet, curator at the Archæological and Pre-historic Museum of Saint-Germain--one of the best-informed men we have in all questions relating to the antiquity of man. In M. de Mortillet's opinion, navigation, both marine and inland, was in actual existence during the polished-stone epoch. [Illustration: Fig. 126.--The earliest Navigators.] The earliest boats that were made by man consisted simply of great trunks of trees, shaped on the outside, and hollowed out in the interior. They were not provided with any rests or rowlocks for the oars or paddles, which were wielded by both hands. In hollowing out the tree they used both their stone implements and also the action of fire. In the earliest boats, the trunk of the tree, cut through at the two ends as well as their imperfect tools allowed, preserved its original outward form. The boat, in fact, was nothing but the trunk of a tree first burnt out and then chipped on the inside by some cutting instrument, that is, by the stone-hatchet. Some improvement subsequently took place in making them. The outside of the tree was also chipped, and its two ends, instead of being cut straight through, were made to terminate in a point. In order to give it more stability in the water and to prevent it from capsizing, it was dressed equally all over, and the bottom of the canoe was scooped out. Cross-stays were left in the interior to give the boat more solidity, and perhaps, also, to serve as a support to the back, or, more probably, to the feet of the rowers, who sat in the bottom of the canoe.