Isle Royale, an island in Lake Superior, forming part of Keweenaw co., Michigan, 55 m. N. W. of Keweenaw point, 15 m. from the Canada shore, intersected by the 48th parallel and the 89th meridian; length from N. E. to S. W. about 45 m., greatest breadth 9 m.; area, 225 sq. m. It has no permanent population. The shores are generally rocky and broken, with several deep inlets. A large number of rocky islets are clustered about it, especially off the N. E. and S. W. extremities. Much of the island is covered with trees, and a longitudinal ridge rises at some points more than 700 ft. above the lake. Extensive veins of native copper have recently been discovered on this island, many of which have been worked by some ancient people, whose stone hammers and copper knives and other tools are found in great numbers in the pits. Some of the excavations on the N. side extend continuously more than two miles, and are connected by underground drains, one of which was cut through rock for a distance of 60 ft., and had been covered throughout with large timbers, now broken and decayed. The stone hammers weigh from 10 to 30 lbs., some of them having a groove for a handle, and the copper tools have been hardened by fire.

The miners exhibited great skill in tracing the veins, and followed the deposits of sheet-like copper, rejecting the nuggets. Some copper arrowheads have been found on the island, and a rude wooden bowl 3 ft. in diameter. At an indentation which forms a good harbor on the S. side, where a stream 40 ft. wide has cut a passage through the rocks and forms a considerable cataract, the apparent site of an ancient town has been discovered. It was on an elevated slope overlooking the lake. No human remains have been found. At least one generation of immense forest trees has grown over all the mines. One is now worked by a New York company. A few deer frequent the island, and it is overrun with rabbits.