[216] Dr. John Bigsby, in a memoir read before the London Geological Society, has described and figured several of these. In a memoir by Charles Stokes, Esq., of London, read before this Society in June, 1837, some of its most striking fossils are figured and described, with references to the prior discoveries of Dr. Bigsby, Captain Bayfield, and Dr. Richardson. Six new species of the Arctinoceras, and five of the Huronia, Ormoceras, and Orthocerata, are figured and described in the most splendid manner. This memoir is essential to all who would understand its fossil history, and that of the North generally. STRAITS OF ST. MARY'S.--These straits, and the river which falls into their head, connect Lakes Huron and Superior. They appear to occupy the ancient line of junction between the great calcareous and granitic series of rocks on the continent. The limestone, which has been noticed along the north shore of the Huron from Michilimackinac, and which continues, with interruptions of water only, from Detour to Drummond Island, and the Manatoulines, is to be noticed up the straits as high as Isle a la Crosse, where the last locality of a pure carbonate of lime appears to occur. The island of St. Joseph is chiefly primitive rock, and its south end is heavily loaded with granitic, porphyritic, and quartz boulders. The north shores of the river, opposite and above this island, are entirely of the granitic series, which continues to Gros Cape of Lake Superior. On reaching the _Nebeesh_,[217] or Sailor's Encampment Island, sandstone rocks of a red color present themselves, and are found also on the American side of the river, and continue to characterize it to the Falls, or Sault de Ste. Marie,[218] and to Point Iroquois and Isle Parisien in Lake Superior. [217] Strong water. [218] Reached somewhere about 1641, by the French missionaries. The Sault of St. Mary's is _upon_ and _over_ this red sandstone. The river makes several successive leaps, of a few feet at a time, in its central channel, falling, altogether, about twenty-two feet in half a mile. This gives it a foaming appearance, and the volume pours a heavy murmur on the ear.[219] It is, of course, a complete interruption to the navigation of vessels, which can, however, come to anchor near its foot, while barges may be pushed up, empty, on the American shore. The water-power created by such a change of level, is such as must commend the spot, at a future period, to manufacturers, lumbermen, and miners. The foot of these falls is heavily incumbered, both with masses of the disrupted sand-rock[220] and granitic and conglomerate boulders.