What the Northern Indians received in exchange for the copper has always been a mystery to me. In Wisconsin and Michigan where drift copper occurred in large quantities, and where it still may be found, it is likely that the natives carried on an extensive trade in copper and that the peoples of Ohio passed it on, one may suppose, to the South. This trade was extensive because not only in our museums are there thousands of copper objects, but there are many more in the hands of private collectors, and in the mounds of the Mississippi Valley where there has been much digging, great quantities of hatchets, plates, nose-rings, and spools are dug up from time to time. [Illustration: FIG. 624. (S. 1–3.) Mica ornaments from mounds of the Hopewell Group. Field Museum collection, Chicago. ] One may question whether the presence of copper in the Ohio Valley really means extensive aboriginal commerce or trade. I say Ohio Valley because more mound copper is found there than elsewhere, although the South should by no means be excluded. Copper and other foreign materials abound in the middle and lower Mississippi Valley. Yet upon the shores of Lake Superior, about the copper range, on the streams and lakes of Wisconsin and Michigan where lived the Indians who possessed so much copper that they made of it hatchets, fish-hooks, knives, spear-points, etc., usually are to be found no Southern types save a few pipes and problematical forms in slate. What did these Northern natives receive in return for the quantities of copper which they must have bartered? Did they receive bird-stones, gorgets, pipes, etc.? Their bird-stones are very like those of Indiana and Ohio, yet they have a broad bird effigy usually with ears on both sides of the head which is not found save occasionally in southern Ohio and Indiana, and seldom in the South where mound copper is common. Their gorgets and pipes appear to be local. It has occurred to me that the peoples of Indiana and Ohio, and possibly the South, made raids in the copper country, or found copper nuggets in the drift, or mined their own copper, or robbed the Northern peoples of such copper as they wanted. If there had been any extensive aboriginal trade, we should surely find more evidence of it. Mr. Clarence B. Moore[28] has conclusively proved that the copper taken from the Southern mounds and Ohio mounds is prehistoric and not of European origin. Some of the gentlemen connected with the Smithsonian Institution and affiliated museums contend that the fine _repoussé_ work, on sheet-copper, could not have been made by aborigines working with stone tools.