But while the remains of extinct species thus serve to determine the periods at which certain eras had their close, the traces of living or extinct fauna are no less valuable as fixing the geographical origin of the ancient colonists, amid whose relics they are found: just as the elephants, the camels, the monkeys, and baboons of the Nimrod obelisk, or the corresponding sculptures on the walls of Memphis or Luxor, indicate the countries whence tribute was brought, or captives were carried off, to aggrandise their Assyrian or Egyptian conquerors. Among relics which help to fix the geographical centres of ancient arts, the sources of early commerce, or the birthplaces of migrating races, might be noted the tin and amber of the Old, and the copper of the New World. So also the Mexican obsidian, the clay-slate of Columbia, the favourite red pipe-stone, or _Catlinite_, of the Couteau des prairies, and the pyrulæ and conch-shells of the Gulf of Florida, indicate varied sources of ancient trade or barter, and lines of migration extending over fully twenty degrees of latitude. Objects wrought in the favourite materials brought from such remote sources have been found mingling with relics of ancient tribes in the islands and on the north shores of the great Canadian lakes, along the southern slope of the same water-shed whence the Moose and the Abbitibbe pour their waters into the frozen sea of Hudson’s Bay. The designation of any primitive stage of industrial arts as a Stone Period signifies, as has been already sufficiently indicated, that condition in which, in the absence of metals, and the ignorance of the simplest rudiments of metallurgy, man has to find materials for the manufacture of his tools, and the supply of his mechanical requirements, in the commoner objects which nature places within his reach.