SUPERIOR, LAKE, the extreme W. and most extensive of the great lakes of the St. Lawrence basin, in North Amer ica, being the largest existing body of fresh water. It is of a triangular form, extending between lat. 40° 30' and 49° N., and lon. 80° and 20' W. Its length, E. to W., is about 360 miles, with a mean breadth of about 80 miles, so that its area may be taken at about 28,600 square miles. The mean depth is estimated at 900 feet, and the height of its surface at about 640 feet above the Atlantic. It receives upward of 50 rivers, but none is of much importance except the St. Louis which enters at its S. W. extremity, and the Riviere au Grand Portage. During the melting of the snow, these and the other rivers sweep into the lake vast quantities of sand, bowlder stones, and drift timber. It discharges itself at its E. extremity into Lakes Huron and Michigan, by the river and falls of St. Mary. This lake embosoms many large and well-wooded islands, the chief of which is Isle Royal. The country of the N. and E. is a moun tainous embankment of rock, from 200 to 1,500 feet in height; the climate unfavor able, and the vegetation slow and scanty. On the S. the land is also high, generally sandy, sterile, and the coast dangerous, subject to storms, and sudden transitions of temperature, and to fogs and mists. The mean heat in June and July is about 65° F., but an extremely cold winter prevails.
The boundary line between Canada and the United States passes from Lake Huron up the river St. Mary, the outlet of Lake Superior, through the center of the lower half of this lake, to the mouth of Pigeon river on the N. shore, between Isle Royal and the Canadian coast. The S. coast of the lake from the outlet to Montreal river belongs to the upper pen insula of Michigan. From this river to the St. Louis river at Fond du Lac the coast belongs to Wisconsin, and thence around to Pigeon river to Min nesota. Toward each extremity the lake contracts in width, and at the lower end terminates in a bay which falls into the outlet, the St. Mary's river, at the two
opposite headlands of Gros Cape on the N. and Point Iroquois on the S. Thence to the mouth of the St. Mary's at Lake Huron is about 60 miles. The navigation of this river is interrupted 20 miles be low its source at the Falls of St. Mary, or, as the place is commonly called, Sault Ste. Marie. Here the river descends in a succession of rapids extending of a mile, from 18 to 21 feet, the fall vary ing with the stage of the water in Lake Superior.
A ship canal has been constructed past the falls by the United States Govern ment, so that now the lake is accessible to vessels from the Atlantic Ocean. The rocks around the lake are very ancient, belonging principally to the Laurentian and Huronian systems of the Azoic series, overlaid in some places, especially on the S. side, with patches of the Lower Silurian. The prevalent Laurentian rock is orthoclase gneiss. Among the Huron ian rocks are greenstones, slates, con glomerates, quartzites, and limestones. The Lower Silurian rocks are soft sand stones. There is everywhere much evidence of glacial action. The Huronian rocks are well stored with useful miner als. The copper and iron mines of the S. side are celebrated for their extent and richness. The richest copper mines are situated near Kee-wee-naw Point. The metal occurs principally native, and sometimes in single masses of great size. Native silver is found associated with the native copper, and sometimes intimately mixed with it. Gold has been found in small specks at Namainse on the British side. Lead ore occurs in some places. The beds of hematite, or red iron ore, at Marquette, on the American side, are of wonderful extent. The water of Lake Superior, remarkable for its coldness, purity, and transparency, is inhabited by many kinds of fish, among which are the delicious white fish and the gray trout.