Lake Superior

SUPERIOR, LAKE, the most north-westerly of the Great Lakes of North America, and one of the largest bodies of fresh water in the world, is bounded on the east and north by the Province of Ontario, on the west by the State of Minnesota, and on the south by Wisconsin and Michigan.

Physiography.—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 i6o miles. Its maximum recorded depth is 1,180 ft., and its mean height above sea-level 602 f t., about 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 49,080 sq.m., the total area of its basin, including the water surface of the lake, being 80,900 sq. miles. 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 inter national 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 Royale, 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 Che quamegon bay.

The boundary between the United States and Canada follows a median line approximately to about mid-lake ; thence it sweeps north-westward, so as to include Isle Royale 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 U.S. territory.

Resources of Region.

The Lake Superior region is 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 Royale, and rich copper mines are worked on the south shore, while nickel abounds in regions of the country north of the lake.

Coasts and Currents.

It has a picturesque coastline, the north shore particularly being indented by deep bays surrounded by high cliffs; the islands also rise abruptly to considerable heights, the north shore furnishing 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 varia tion, covering a cycle of years, being about 4 feet. The discharge of the lake is computed to be 75,200 cu.ft. per second at mean stage of water, and is controlled by dikes and sluice gates at the head of St. Mary's falls.

Navigation.

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 Decem ber. 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.