Disembarking from the steamer and traveling inland at any point where the shores are high, the traveler is certain to come upon still more convincing proofs of the ancient strands; perhaps in a storm beach of the unmistakable “shingle”, half buried though it may be under dunes of newly drifted sand, or possibly at higher levels the highway has been cut through a shingle barrier as fresh and unmistakable as though formed upon the present shore. Sometimes it is the rock cliff and terrace, at other times barrier ridges of shingle, or, again, it is the sloping cliff and terrace cut in the drift deposits; but of whatever sort, if studied with proper regard to the topography of the district, the evidence is clear and unmistakable.
The records of uplift about Mackinac Island.—Nowhere are the records of the recent uplift of the lake region more easily read than about Mackinac Island in the straits connecting Lake Michigan with Lake Huron. Approaching the island by steamer from St. Ignace, its profile upon the horizon is worthy of remark ([Fig. 369]). From a central crest broken by minor irregularities and bounded on all sides by a cliff, the island profile slopes gently away to a still lower cliff, below which is another terrace.
Fig. 369.—View of Mackinac Island from the direction of St. Ignace. The irregular central portion is the only part of the island that was not submerged in Lake Algonquin. The terrace at its base is the old shore line of Lake Algonquin, and the lower terrace the strand of Lake Nipissing (after a photograph by Taylor).
Fig. 370.—The “Sugar Loaf”, a stack near the shore of Lake Algonquin, as it is seen from the observatory upon Mackinac Island (after a photograph by Taylor).
When we have reached the island and have climbed to the summit, we there find the surface which is characteristic of erosion by running water, whereas at lower levels are found the forms carved or molded by the action of waves. This central “island”, superimposed upon the larger island, is all that rose above Lake Algonquin, the earliest of the glacial lakes in this northern district; and as we look out from the observatory upon the summit, it is easy to call up a picture of the country when the lake stood at the base of this highest cliff. To the northward one sees the “Sugar Loaf” rise out of a sea of foliage, as it formerly did from the waters of Lake Algonquin ([Fig. 370]). It is a huge stack near the former island shore. If we turn now to the southward and direct our gaze toward the Fort, we encounter a veritable succession of beach ridges formed of shingle and ranged like a series of waves within the cleared space of the “Short Target Range” ([Fig. 371]). These ridges mark each a stage within a series of successive uplifts which have brought the island to its present height.
Fig. 371.—View from the observatory upon Mackinac Island across the “Short Target Range” toward the Fort. Beach ridges appear in succession within the cleared space (after a photograph by Rossiter).
