In the history of primitive man in North America, we shall have to invent another age of a special character; this is the _Age of Copper_. In America, the use of copper seems to have preceded the use of bronze; native metallic copper having been largely in use among certain races. On the shores of Lake Superior there are some very important mines of native copper, which must have been worked by the Indians at a very early date; in fact, the traces of the ancient workings have been distinctly recognised by various travellers. Mr. Knapp, the agent of the Minnesota Mining Company, was the first to point out these pre-historic mines. In 1847, his researches having led him into a cavern much frequented by porcupines, he discovered, under an accumulation of heaped-up earth, a vein of native copper, containing a great number of stone hammers. A short time afterwards, some other excavations 25 to 35 feet in depth, and stretching over an extent of several miles, came under his notice. The earth dug out had been thrown on each side of the excavations; and mighty forest-trees had taken root and grown there. In the trunk of a hemlock-tree growing in this "made ground," Mr. Knapp counted 395 rings of growth, and this tree had probably been preceded by other forest-giants no less venerable. In the trenches themselves, which had been gradually filled up by vegetable _débris_, trees had formerly grown which, after having lived for hundreds of years, had succumbed and decayed; being then replaced by other generations of vegetation, the duration of which had been quite as long. When, therefore, we consider these workings of the native copper-mines of Lake Superior, we are compelled to ascribe the above-named excavations to a considerable antiquity. In many of these ancient diggings stone hammers have been found, sometimes in large quantities. One of the diggings contained some great diorite hatchets which were worked by the aid of a handle, and also large cylindrical masses of the same substance hollowed out to receive a handle. These sledges, which are too heavy to be lifted by one man alone, were doubtless used for breaking off lumps of copper, and then reducing them to fragments of a size which could easily be carried away. If we may put faith in Professor Mather, who explored these ancient mines, some of the rocks still bore the mark of the blow they had received from these granite rollers. The work employed in adapting the native copper was of the most simple character. The Indians hammered it cold, and, taking into account its malleable character, they were enabled with tolerable facility to give it any shape that they wished.