For example, we may infer that if the craftsman who made an eagle-beaked tool showed intelligence in some other useful ways, he did no more than common justice to his humanity. Suppose he cut down a tree with his flint axe, choosing one that grew aslant over a chasm or across a river; or suppose he piled stepping-stones together in the middle of a waterway, and then used this pier as a support for two tree-trunks whose far ends rested on the banksides. Neither of these ideas has more mother-wit than that which has enabled ants to bore tunnels under running water, and to make active bridges by clinging to each other in a suspension chain of their wee brave bodies. Not many human minds in any period of history have been as diligently rational as ants; but let us risk the conjecture that the first advance in bridge-making began among the rostro-carinate workmen probably more than half a million years ago. To cut down a tree, in order to get a bridge at a chosen place, was a good idea in primitive enterprise, but it was not enough; it gave but little additional help in tribal wars, since it repeated the narrow footway, the main drawback of windfall tree-bridges. Two or three trees laid side by side were necessary, and at least two piles of stepping-stones to carry enough trees over a fairly wide river. Such were the first improvements that war and social life demanded from the wit of primitive mankind, and often they were demanded in vain for many long ages. Even at the present time there are tribesmen who feel well pleased with themselves when they make single and double tree-bridges. I am told, for instance, by Mr. T. Beddoes, a traveller and trader in Equatorial Africa, that often in his wanderings he has made and used a tree-bridge to cross a narrow creek, following a native method for the sake of its ready convenience. “The natives,” he writes, “cut down the tallest trees on a bank of the waterway that they intend to bridge, then they make a handrail with bush-rope fastened to short upright sticks which are placed about three feet apart. Bush-rope is made from creepers or from long cane vines. Sometimes an attempt is made to flatten the upper surface of the tree; but this work is uncommon, as African natives are lazy; they detest manual labour. There are trees that grow to an enormous height; one of them measured a hundred feet odd, so fairly wide creeks and streams can be bridged. But canoes are the favourite means of crossing rivers; they carry light loads well enough, and they need less labour than bridge-building.”