The savage can fasten only a dozen pounds on his back and swim the river. When he makes an axe, fells a tree, and builds a raft, he can carry many times a dozen pounds. As soon as he learns to rip logs into boards and build a boat, he multiplies his power a hundredfold; and when to this he adds modern sciences he can produce the monster steel leviathans that defy wind, storm and distance, and bear to the uttermost parts of the earth burdens a millionfold greater than the savage could carry across the narrow river."