Longitude of Detroit, calculated from above 82 54 53 Latitude of camp near head of Lake Michigan, Aug. 31 and Sept. 1 41 38 48 Mean latitude of the extreme south point of Lake Michigan, 4 sets of observations and meridian observation 41 37 28 Latitude of camp next north of the St. Joseph's, near Kekalamazo, Sept. 3 42 32 16 Latitude of camp at Maskegon River, Sept. 4 43 13 41 Latitude of camp near Point aux Salles, Lake Michigan, Sept. 5 44 5 17 Latitude of camp at Grand Traverse Bay, Lake Michigan, Sept. 7 45 34 24 [203] _Galet_, in the Canadian patois, means a smooth, flat rock.--H. R. S. [204] A little doubtful. [205] A little doubtful. [206] Or 20´´. 3. MINERALOGY AND GEOLOGY. VI. _Report on the Copper Mines of Lake Superior._ By HENRY R. SCHOOLCRAFT. To the Hon. JOHN C. CALHOUN, _Secretary of War_. VERNON (Oneida County, N. Y.), November 6, 1820. SIR: I have now the honor to submit such observations as have occurred to me, during the recent expedition under GOV. Cass, in relation to the copper mines on Lake Superior; reserving, as the subject of a future communication, the facts I have collected on the mineralogy and geology of the country explored generally. The first striking change in the mineral aspect of the country north of Lake Huron, is presented near the head of the Island of St. Joseph, in the River St. Mary, where the calcareous strata of secondary rocks are succeeded by a formation of red sandstone, which extends northward to the head of that river at Point Iroquois, producing the falls called the _Sault de Ste. Marie_, fifteen miles below; and thence stretching northwest, along the whole southern shore of Lake Superior, with the interruptions noted, to Fond du Lac. This extensive stratum is perforated at various points by upheaved masses of sienitic granite and trap, which appear in elevated points on the margin of the lake at Dead River, Keweena Point, Presque Isle, and the Chegoimagon Mountains. It is overlaid, in other parts, by a stratum of gray or neutral-colored sandstone, of uncommon thickness, which appears in various promontories along the shore, and, at the distance of ninety miles from Point Iroquois, constitutes a lofty perpendicular and caverned wall, upon the water's edge, called the Pictured Rocks.