SUPERIOR, LAKE. The largest and most northerly of the Great Lakes of North America, and the largest body of fresh water in the world (Map: America, North, K 5). It is situated a little to the northeast of the centre of the conti nent, and is bounded on the north and east by the Canadian Province of Ontario, and on the south by the State of Michigan and a part of :Minnesota, the latter State forming also the western boundary. Its shape is nearly a cres cent, the horns extending southwest and south east, while the large Keweenaw Peninsula reaches nearly to the centre of the lake from the middle of the southern coast. Lake Superior has a coast line of 1500 miles: its extreme length from east to west is 412 miles; its extreme breadth is 167 miles. Area, 31,200 square miles. Its mean elevation above sea level is 602 feet, and it lies 20 feet above the level of Lake Huron, into which it discharges through the Saint Mary's River (q.v.). It receives a large number of streams, hut they are all short, the basin of the lake being closely hemmed in by the water sheds of the Mississippi and of Hudson Bay.
The principal stream entering it is the Saint Louis River, which falls into the extreme western end of the lake, and is considered as the farthest headstream of the Saint Lawrence.
The shores of Lake Superior, except in the southeast, where there are long lines of sand dunes, are generally bold and rocky. On the Michigan shore are the celebrated sandstone chills known as Pictured Rocks, which are streaked by the red and yellow deposits of fer ruginous waters. In many places, especially along the Canadian shore, there are precipitous cliffs of basalt rising directly from the water to a sheer height of from 300 to over 1000 feet, such as Thunder Cape on the northwest shore. The north shore is also cut up into deep bays sur rounded by high cliffs, and forming good har bors, and it is lined with a number of high, rocky islands with precipitous sides and capped by eruptive material. In the greater part of the lake, however, the islands are few, the largest being Isle Royal, 45 miles long and 8 miles wide, belonging to Michigan. In general the country
surrounding the lake is covered with pine forests.
Lake Superior is deeper than any of the other Great Lakes, its maximum depth being 1008 feet, so that the bottom lies 400 feet below sea level. The water is very clear, and so fresh as to be al most chemically pure. It is cold throughout the year to within a few feet of the surface, and in the deeper portions maintains a nearly uni form temperature of 39°. The lake never freezes except in the shallow water along the shores. The level of the lake is subject to several sets of periodic changes, partly owing to changes in rainfall and evaporation and partly to the winds; a long continued storm will sometimes raise the leeward level seven feet above the nor mal. Violent storms occasionally sweep over the lake, when the waves may attain an amplitude of 15 or 18 feet.
The basin of Lake Superior is remarkable as being unrelated to those of the other Great Lakes. While the latter are river valleys scooped out of the softer strata of the ancient coastal plain lying northwest of the Appalachian Plateau and skirting the Archa'an continent, Lake Su perior lies almost wholly within the Archnan region. The most recent investigators are of the opinion that this basin is a primitive depression in the earth's crust antedating the Huronian pe riod. The numerous intrusions of eruptive rocks which encircle the lake are arranged roughly in concentric circles, the most recent being found nearest the lake, and it has been suggested that the depression is an ancient and deep-seated cen tre of volcanic. activity. The formation of the lakes themselves, however, is due to the obstruc tion of the valleys during the Glacial Period. The country surrounding the lake is rich in min erals, and large veins of copper and iron ore traverse its bottom from the southern shore. Consult Agassiz, Lake Superior: Its Physieat Character, Vegetation, and Animals (Boston, 1850). For commerce and navigation on the lake, see GREAT LAKES.