In the first volume of his book, chap. VII., Antonio de Ulloa visits the Andes, and finds there some tree-bridges, some stone bridges, and some complex bujuco bridges. The stone variety he does not describe, but he writes interestingly about the bujucos. When six cables have been made by twisting together strips of ox-hide they are suspended across a river, not in a single row, but in two tiers, the lower one with four cables, the upper with two. Over the lower tier branches and canes are laid transversely; and when this floor is braced to the upper cables, there is a sort of cage within which travellers can walk in safety while the bridge swings. “On some rivers of Peru,” says Ulloa, “there are bujuco bridges so large that droves of loaded mules pass over them; particularly over the river Apurimac, which is the thoroughfare of all the commerce carried on between Lima, Cusco, La Plata, and other parts to the southward.” Humboldt passed over one of these pendulous bridges, and Miers crossed another which was strong enough to bear the traffic of pack-mules, though it was two hundred and twenty-five feet in span. And now we must pass on to a half-suspension bridge which is very common among the N’Komis, a tribe that inhabits the Fernan Vaz district in Equatorial Central Africa. It is a bridge built with Y-shaped sticks. Two parallel rows of these pronged branches are driven into the bed of a stream, and into the banksides; then long runners are put between the forks to bear a footway of sticks laid across them transversely. Mr. Thomas Beddoes, an African trader, and traveller, draws my attention to this bridge of forked branches; and tells me also that in the Agowe district, but far inland from the banks of this river, he came upon a primitive suspension bridge partly made with very thick vines--vines as thick as a man’s leg--which were joined together into a couple of natural ropes long enough to be suspended from trees over a creek about two hundred feet wide. Perhaps a yard separated them, and they were parallel to each other. When anchored to the trees at a height of four or five feet above the bank, they form the upper part or parapet of the bridge. As for the footway, its bearers were saplings--young trees from ten to twelve feet long and three or four inches in diameter; they were lashed together into a continuous runner, and two such runners were laid from the banksides over the creek, to carry a hurdle pathway of canes or sticks. Then the upper part of the bridge was braced to the saplings with thin vines, which were tied to their supports at intervals of about a foot, and which served the purpose of suspension rods, for they counteracted the strain on the saplings when a native crossed the narrow footway. It would be easy to write much more about primitive swing bridges, but enough has been said to stimulate thought and discussion. Not one of them has a brighter intelligence than that which we find in many prehistoric handicrafts.