In the month of March, 1848, Samuel O. Knapp and J.B. Townsend discovered, from tracks in the snow, that a hedgehog had taken up his winter-quarters in a cavity of a ledge of rocks, about twelve miles from Ontonagon, Lake Superior, in the neighborhood of the Minnesota Copper Mine. In order to capture their game, they procured a pick and shovel, and commenced an excavation by removing the vegetable mould and rubbish that had accumulated about the mouth of what proved to be a small cavern in the rock. At the depth of a few feet they discovered numerous stone hammers or mauls; and they saw that the cavern was not a natural one, but had been worked out by human agency, and that the stone implements, found in great profusion in and about it, were the tools used in making the excavation. Further examination developed a well-defined vein of native copper running through the rock; and it was evidently with a view of getting this metal that this extensive opening had been made. This was the first instance where "ancient diggings"--as they are familiarly called in the Lake Superior region--were ever recognized as such; and this artificial cavern presents the most conclusive proofs that a people in the remote past worked those mines. Upon the discovery of this mine, attention was at once directed to numerous other cavities and depressions in the surface of the earth at this and other points, and the result was that nearly a hundred ancient pits were found, and in all of them mining-tools of various kinds. These ancient mines or pits are not restricted to one locality, but extend over the entire length of the copper region, from the eastern extremity of Keweenaw Point to the Porcupine Mountains, a distance of nearly one hundred miles. In some of the ancient diggings, the stone hammers have the marks of hard usage, fractured or battered faces, and a large proportion of them are broken and unfit for use; but in other pits the hammers are all sound, and many of them have the appearance of never having been used. These hammers, or mauls, which are of various sizes, and not uniform in shape, are water-worn stones, of great hardness, similar in all respects to those that are found in abundance on the shore of the Lake, or in the gravel-banks of that region. They are generally trap-rock, embracing the varieties of gray, porphyritic, hornblendic, sienitic, and amygdaloidal trap, and appear to have had no labor expended upon them except the chiselling of a groove around the middle for the purpose of attaching a withe to serve as a handle. In a few instances, I have noticed small hammers, usually egg-shaped, without a groove; and the battered or worn appearance at one end was all that induced the belief that they were ever used for hammering.