Mr. Squier says, "These articles have been critically examined, and it is beyond doubt that the copper bosses were absolutely plated, not simply overlaid, with silver. Between the copper and the silver exists a connection such as, it seems to me, could only be produced by heat; and if it is admitted that these are genuine relics of the Mound Builders, it must, at the same time, be admitted that they possessed the difficult art of plating one metal upon another. There is but one alternative, viz., that they had occasional or constant intercourse with a people advanced in the arts, from whom these articles were obtained. Again, if Dr. Hildreth is not mistaken, oxydized iron or steel was also discovered in connection with the above remains, from which also follows the extraordinary conclusion that the Mound Builders were acquainted with the use of iron, the conclusion being, of course, subject to the improbable alternative already mentioned." In connection with this subject, we would refer to the interesting evidences that the copper mines of the shore of Lake Superior had been at some very remote period worked by the Mound Builders. There were found deep excavations, with rude ladders, huge masses of rock broken off, also numerous stone tools, and all the evidences of extensive and long-continued labor. It is even said that the great Ontonagon mass of pure copper which is now in Washington was excavated by these ancient miners, and that when first found its surface showed numerous marks of their tools. There seems to be no doubt, then, that the Mound Builders were familiar with the use of copper, silver, and lead, and in all probability of iron. They possessed various mechanical contrivances. They were very probably acquainted with the lathe. Beads of shell have been found looking very much like ivory, and showing the circular striæ, identical with those produced by turning in a lathe. In a mound on the Scioto River was found around the neck of a skeleton triple rows of beads, made of marine shells and the tusks of some animal. "Several of these," says Squier, "still retain their polish, and bear marks which seem to indicate that they were turned in some machine, instead of being carved or rubbed into shape by hand."