Lake Huron, one of the great lakes on the boundary between the United States and British America, lying between lat. 43° and 46° 15' N., and Ion. 80° and 84° 40' W. It receives at its N. extremity the waters discharged from Lake Superior by St. Mary's river or strait, and also those of Lake Michigan through the strait of Mackinaw. Its outlet at the S. extremity is the St. Clair river. It is bounded W. and S. W. by the southern peninsula of Michigan, N. and E. by Ontario, Canada. Georgian bay, 120 m. long and 50 m. wide, lies wholly within Ontario, and is shut in from the main body of the lake by the peninsula of Cabot's head on the south and the Manitoulin chain of islands on the north; and N. of these islands is Mani-tou bay or the North channel. The whole width of Lake Huron, including Georgian bay, is about 190 m., and its length about 250 m. Its area is computed to be about 21,000 sq. m. Its elevation above the sea is rated by the state engineers of Michigan at 578 ft.; the Canadians make it 3 ft. less. The level of its waters fluctuates several feet at irregular periods, as is observed also of the other lakes. Various estimates are made of its average depth, the least being 800 ft., and the highest, which is that of the Michigan state report of 1838, 1,000 ft.

In this report it is stated that soundings have been made in the lake of 1,800 ft. without finding bottom. Few harbors are found along the W. shore of Lake Huron. About 70 m. N. of the outlet Saginaw bay sets back into the land a distance of 60 m. toward the S. W., and under its islands and shores vessels find shelter from the storms which prevail from the N. E. or S. W. up and down its wide mouth and across the broadest expanse of the lake. Thunder bay is a much smaller extension of the lake into the land, about 140 m. from the outlet. Steamers usually stop here for supplies of wood, chiefly pine and birch, which, with the white pine largely cut for lumber, and excellent grindstones obtained from the sandstone rocks, constitute the only valuable products of these shores. At Presque Isle, 28 m. further N., is another harbor, where the land turns round toward the N. W., and a straight course is thence made for Mackinaw, 70 m. distant. This island is famous as a trading post and fort in the history of the northwest and of the fur trade, and is still a point of importance on the lake. The harbor is deep and well sheltered, on the S. side of the island, under high hills, upon which stands the United States fort.

The fishing business is extensively carried on, white-fish of excellent quality abounding in the lake near by, and those of the northern part of Lake Michigan also finding a market here. - The shores on the Michigan side present few features of interest. The rock formations are sandstones and limestones of the several groups from the Helderberg to the coal measures, the latter being found in the upper portion of Saginaw bay, where, however, they are of little importance. Beaches of sand alternate with others of limestone shingle, and the forests behind are often a tangled growth of cedar, fir, and spruce in impenetrable swamps, or a scrubby scattered growth upon a sandy soil. Calcareous strata of the upper Silurian stretch along the E. coast from the outlet nearly to Georgian bay, and are succeeded by the lower members of the same series down to the Hudson river slates and the Trenton limestone, which last two stretch across from Lake Ontario to Georgian bay. In the metamorphic rocks found in the upper portions of Manitou-lin bay copper ores begin to appear, and have been worked at the Bruce mines.

With the change in the rock formations the surface becomes more broken and hilly, rising to elevations 600 ft. or more above the lake. - The rivers that flow into Lake Huron are mostly of small importance. The principal streams from Michigan are Thunder Bay river, the Au Sable, and the Saginaw; from Ontario, the French (outlet of Nipissing lake), the Muskoka, the Severn (outlet of Lake Simcoe), and the Notta-wasaga, all emptying into Georgian bay, and Saugeen, Maitland, and Aux Sables. The chief towns on its shores are Collingwood and Owen Sound (on Georgian bay), Goderich, and Sarnia (at the entrance of St. Clair river), in Ontario; in Michigan, Bay City at the head of Saginaw bay, and Port Huron opposite Sarnia. The season of navigation in Lake Huron is usually from the last of April or early part of May into December; and the finest season, during which the waters often continue smooth and the air mild and hazy for two or three weeks, is the latter portion of November.