The contents of the earthworks of the Ohio and Mississippi valleys show that the copper, found in a pure metallic condition at various points around Lake Superior, was not unknown to their constructors. But in this they had little advantage over the Iroquois and Algonkin tribes, in whose grave mounds copper axes and spear heads occasionally occur. It is even possible that working parties were despatched from time to time to the ancient copper mines on the Kewenaw peninsula, on Lake Superior, to bring back supplies of the prized malleable rock, which could be bent and hammered into shape in a way that no other stone was susceptible of. But the labours of the native miners were inadequate to provide supplies that could in any degree suffice to displace the flint or quartzite of the implement-maker. One use, however, has been suggested for the copper, in relation to the labours of the flint-workers. Mr. George Ercol Sellers, whose researches among the workshops of the ancient tool-makers have thrown much light on their processes, was led, from careful observation of some of their unfinished work, to the opinion that copper was in special request in the operations of the flint-flaker. After referring to the well-known use of horn or bone-flakers, he thus proceeds: “From the narrowness of the cuts in some of the specimens, and the thickness of the stone where they terminate, I have inclined to the belief that, at the period they were made, the aborigines had something stronger than bone to operate with, as I have never been able to imitate some of their deep heavy cuts with it; but I have succeeded by using a copper point, which possesses all the properties of the bone, in holding to its work without slipping, and has the strength for direct thrust required.”[27] No copper tool, however, was recovered by Mr. Sellers among the vast accumulations of implements and waste chips, hereafter described, on the sites of the ancient workers’ industrious operations, though some of those found elsewhere may have been used for such a purpose.