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Page:Popular Science Monthly Volume 19.djvu/622

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about five inches in diameter, though some are eight and even ten inches, and of a rounded oval outline. They were certainly gathered as pebbles along the shore of the lake, north from the island, where there are still others of the same shapes and sizes, and of the same varieties of

PSM V19 D622 Rawhide string and knot from the isle royale mines.jpg

Fig. 4.—Raw-hide String and Knot of the Isle Royale Ancient Miners.

rock, formed on the beach by the action of the waves. The great profusion in which they are scattered among the débris of the pits would itself indicate the ease with which they were obtained. They are not grooved for the reception of a withe, like those found on the south shore, near Ontonagon, but they were apparently used for the most part by simply swinging them in the hand, or probably in both hands clasped, thus by repeated blows breaking away the surrounding rock or hammering the desired metal into such shapes as to facilitate its separation in smaller pieces. The rock of which they are composed does not occur as pebbles on Isle Roy ale, and indeed it is doubtful if it exists at all on the island. It forms the coast of the mainland for several miles opposite the island. It is an igneous rock, visually a diabase, as shown in thin sections under the microscope, consisting essentially of a triclinic feldspar and augite, with magnetite. Sometimes the grains are coarser, and the rock would more properly be styled a dolerite or a gabbro. They belong to the formation designated by Sir William Logan The Lower Volcanic Group, but since styled Animikie Group, by Professor T. S. Hunt.[1] Occasionally, however, the workmen seem to have gathered rounded stones of other varieties of rock, though nothing equaling the firmness of the above, and so fit for the purpose of a rude hammer in simple mining, can be selected among all the rocks of the region. One or two, of a granite containing red orthoclase, were seen at the mine, and a few of other granites are reported to have been found. These other varieties are also seen mingled sparsely with the diabase stones along the Canadian shore, and are referable to the drift forces which transported them from farther north and east in Canadian territory.

Although these hammers, as a rule, are not withed, it is still true that occasionally one is found that is withed—i. e., grooved for the reception of a withe handle. One seen at the time of this visit was owned by Dr. Gailey, and was not well wrought. The groove was evidently

  1. Vide "Trap Dikes and Azoic Rocks of Southeastern Pennsylvania," "Second Geological Survey of Pennsylvania," pp. 68, 240.