Superior

Superior, the most north-westerly of the Great Lakes of North America, and the largest body of fresh water in the world, lying between 46° 30' and 48° N., and 84° 30' and 92° W. It is bounded E. and N. by the province of Ontario, W. by the state of Minnesota, and S. by Wisconsin and Michigan. It has deep, extremely cold, clear water, and high and rocky shores along a large portion of its coast. Its general form is that of a wide crescent convex towards the north, but its shores are more irregular in outline than those of the other lakes. Following the curves of its axis from west to east the lake is about 383 m. long, and its greatest breadth is 160 m. Its maximum recorded depth is 1008 ft., and its height above mean sea level is 602 ft., or about 21 ft. above that of lakes Michigan and Huron, to which it is joined at its eastern extremity through the river St Mary. The lake receives the waters of 200 rivers, and drains a territory of 48,600 sq. m., the total area of its basin being 80,400 sq. m. The largest river which empties into it is the St Louis, at its western end. The principal rivers on the north shore are the Pigeon, which forms the international boundary line, the Kaministikwia, the Nipigon, which drains the lake of the same name and together with the lake is about 200 m. long, the Pic, the White and the Michipicoten. No large rivers empty into Lake Superior from the south. There are not many islands in the lake, the largest being Isle Royal, 44 m. long; Michipicoten Island in the eastern part; St Ignace, in the northern part, off the mouth of the Nipigon River; Grand Island between Pictured Rocks and Marquette; Manitou Island, east of Keweenaw Point, and the Apostle Group, to the north of Chequamegon Bay.

The boundary between the United States and Canada runs up the middle of the outlet of the lake and follows a median line approximately to about mid-lake; thence it sweeps northwestward, so as to include Isle Royal within the territory of the United States, and continues near the north shore, to the mouth of Pigeon River, which it follows westward, leaving the whole west end of the lake in United States territory.

Lake Superior lies in a deep rift in rocks principally of Archean and Cambrian age, of the Laurentian, Huronian and Keweenaw formations, rich in minerals that have been extensively worked. The lake is, as it were, surrounded by iron, which is the probable cause of very strong magnetic. fields of influence. Native silver as well as silver ores exist around Thunder Bay, native copper was formerly worked on Isle Royal, and rich copper mines are worked on the south shore, while nickel abounds in the country north of the lake. The Archean rocks produce a picturesque coast-line, the north shore particularly being indented by deep bays surrounded by high cliffs, mostly burnt off and somewhat desolate; the islands also rise abruptly to considerable heights, the north shore furnish= ing the boldest scenery of the Great Lakes. On the south coast, opposite the broadest part of the lake, are precipitous walls of red sandstone, extending about 14 m., famous as the Pictured Rocks, so called from the effect of wave action on them. There are no appreciable tides and little current. A general set of the water towards the outlet exists, especially on the southern shore. From the Apostle Islands to the eastward of Keweenaw point this current has great width, and towards the eastern end of the lake spreads out in the shape of a fan, a branch passing to the northward and westward reaching the north coast. Autumn storms raise dangerous seas. The level varies with the season, and also from year to year, the maximum variation, covering a cycle of years, being about 5 ft. The discharge of the lake is computed to be 75,200 cubic ft. per second at mean stage of water.

The season of navigation, controlled by the opening and closing of the Sault Ste Marie canals, averages about eight months - from the middle of April to the middle of December. The season has been extended for a few days, in both spring and autumn, by the use of ice-breaking tugs at Fort William and Port Arthur, this service being organized by the government particularly to facilitate the movement of grain from the Canadian North-west. The lake never freezes over, though the temperature of the water does not, even in summer, rise far above freezing point. The bays freeze over and there is border ice, often gathered by wind into large fields in the bays and extremities of the lake.

Lake Superior is fairly well provided with natural harbours, and works of improvement have created additional harbours of refuge at various points. Marquette, Mich., Presque Ile Point, Mich., Agate Bay, Minn., Grand Marais, Minn., and Ashland, Wis., are on bays which have protective breakwaters across their mouths. Duluth, Superior, Port Wing, Wis., Ontonagon, Mich., and Grand Marais, Mich., are harbours with entrances formed by parallel jetties extending across obstructing bars. On the Canadian side Fort William, in the mouth of the Kaministikwia, and Port Arthur, four miles distant, an artificial harbour, are the only important shipping points, being the lake terminals of three great transcontinental railway systems, though the whole north shore is liberally supplied with natural harbours. The traffic on Lake Superior grows constantly in volume, the increase in tonnage of each year over that of the preceding year having, for 50 years past, averaged 20%. The freight carried into and out of the lake, as gauged by the statistics gathered at the Sault Canal offices, aggregated in 1907 over 58,000,000 (short) tons. The principal freight shipped eastward consists of flour, wheat and other grains, through Duluth - Superior from the United States, and through Fort William - Port Arthur from the Canadian prairies; copper ore from the mines on the south shore; iron ore in immense quantities from both shores, ? the principal ore shipping ports being Ashland, Two Harbors, Marquette, Superior and Michipicoten, and lumber produced on the tributary rivers. West-bound freight consists largely of coal for general distribution and for terminal railway points.

The fishing industry of Lake Superior is important, salmon-trout (Salvelinus namaycush, Walb), ranging from 10 to 50 lb in weight, being gathered from the individual fishermen by steam tenders and shipped by rail to city markets. The river Nipigon, on the north shore, is famous for speckled-trout (Salvelinus fontinalis, Mitchill) of unusual size; and all rivers and brooks falling into the lake are trout streams.

See Bulletin No. 17, Survey of Northern and North-Western Lakes, U.S. War Department, Lake Survey Office, Detroit (1907); Sailing Directions for Lake Superior and the St Mary's River, U.S. Hydrographic Office publication No. 108 A. (Washington, 1906), with supplements. (W. P. A.)