Thus, in various localities, remote from native sources of flint, a systematic manufacture of implements appears to have been carried on. There can, therefore, be scarcely any hesitation in inferring, from the evidence adduced, first a trade in the raw material brought from the distant localities of the flint mines; and then a local traffic in the manufactured implements, as was undoubtedly the case among the American aborigines at no remote date. This aspect of primitive interchange, both of the raw material and the products of industrial skill, in so far as it is illustrated in the practice of the American Indian tribes, merits the most careful study, as a help to the interpretation of the archæological evidence pertaining to prehistoric times. To the superficial observer, stone is of universal occurrence; and it seems, therefore, needless to inquire where the implement-maker of any Stone age procured the rough block out of which he fashioned his weapon or tool. Only when copper, bronze, and iron superseded the crude material of the Stone age has it been supposed to be needful to determine the sources of supply. But that is a hasty and wholly incorrect surmise. The untutored savage is indeed greatly limited in his choice of materials. We are familiar with the shell-workers of the Caribbees and the Pacific Islands, and the horn and ivory workers of Arctic regions; but where the resources of an ample range could be turned to account, the primitive workman learned at a very early date to select by preference such stones as break with a conchoidal fracture. Only where such could not be had, the most available chance-fractured chip or the apt water-worn stone was turned to account. Rude implements are accordingly met with fashioned of trap, sienite, diorite, granite, and other igneous rocks, as well as from quartzite, agate, jasper, serpentine, and slate. Some of those materials were specially favoured by the neolithic workmen for certain classes of their carefully finished weapons and implements, such as perforated hammers, large axes, gouges, and chisels. But the natural cleavage of the flint, and the sharp edge exposed by every fracture, adapt it for fashioning the smaller knives, lance and arrow heads, in a way no other material except obsidian equals. Hence flint appears to have been no less in request among ancient tool-makers than copper, tin, and iron in the later periods of metallurgic art.