HIGHLANDS OF SAUBLE.--On crossing the bay, these highlands present themselves to view in the distance. They are the north-eastern verge of the most elevated central strata of the peninsula. Their structure can only be inferred from the formations along the margin of the lake, extending by Thunder Bay and Presque Isle, and the Isles of Bois Blanc and Round Island to Michilimackinac. At Thunder Bay, the compact limestone of the Saganaw Islands reappears, and is constantly in sight from this point to Presque Isle. It exists in connection with bituminous shale, at an island in Thunder Bay. It is of a dark carbonaceous character on the main opposite Middle Island, at a point which is called by the Indians _Sho-sho-ná-bi-kó-king_, or Place of the Smooth Rock. I noticed at this point the cyathophyllum helianthoides in abundance, and easily detached them from the rock. The more compact portions of this formation in the approach to Presque Isle, disclosed the ammonite, two species of the gorgonia, and the fragment of a species of chambered shell, whose character is indeterminate. Much of the coast was footed, as the winds were adverse, and its debris thus subjected to a careful scrutiny. Wherever the limestone was broken up or receded from the water, long lines of yellow beach-sand and lake-gravel, including members of the erratic block stratum, intervened. In some localities, local beds of iron sand occur. MICHILIMACKINAC.[215]--The approach to this island was screened from our view by the woody shores and forests of Bois Blanc, an island of some twelve miles in length lying off the main land; and the view of it first burst upon us in the narrow channel between it and Round Island. It is a striking geological monument of mutations. Here the calcareous rock, which had before exhibited itself in low ledges along the shore is piled up in masses, which reach an extreme altitude of three hundred and twelve feet. About two hundred feet of this elevation is precipitous on its south, east, and west edge. A hundred feet or more is piled up on its centre, part rock and part soil, in a crowning shape. The highest part of this apex, which is surmounted by the ruins of Fort Holmes, consists of the drift stratum, among which are boulders of sienite, and other foreign rocks. A locality of these abraded boulder-rocks, near the Dousman farm, is worthy of a visit from all who take an interest in the phenomena of boulders dispersed over the continent. The fishermen represent the water around this island to be eighty fathoms in depth. Yet, across these waters, to the utmost altitude of the island, these blocks of foreign rock have been transported. No force capable of effecting this is now known. And the argument of their having been transported on cakes of ice, in the nascent periods of the globe, is rendered stronger by these appearances than any geological proofs which I have yet seen.