Lake Superior.—The northern shores of Superior are mostly precipitous cliffs ranging from three hundred to one thousand feet in height. On the southeast sandy coasts prevail. The coast on the south and southwest is composed largely of sandstone cliffs, rich in iron and other metal deposits. The bed of Superior is supposed to be an ancient volcanic crater. Its depth of one thousand and eight feet represents a depression extending four hundred feet below sea-level. Superior is, therefore, distinct in origin from the other lakes of the group, whose beds represent ancient river systems and date from the glacial period. The basin of the lake, closely circumscribed by the Mississippi and Hudson Bay watersheds, receives many streams, but all of them short.
Lake Huron, the second of the Great Lakes, is bounded north, east and south by the Province of Ontario, and south and west by the State of Michigan, including Georgian Bay (five thousand six hundred and twenty-six square miles), and North Passage, one thousand five hundred and fifty-six square miles. It is connected with Lake Michigan by the Straits of Mackinac, three and one-half miles broad and one hundred and thirty-five feet deep.
The discharge of Lake Huron is about two hundred and seventeen thousand cubic feet per second. By reason of evaporation and rainfall, the level of the lake varies annually between four and five feet, but much greater local variation is caused by the strong winds. The densely wooded northeast is broken by many low islands of limestone and glacial débris. Elsewhere the shores are almost unbroken and low, except when cliffs of one hundred or one hundred and fifty feet high rise from the northeast border and afford good sites for the many Canadian towns and villages. Nearly all the harbors on this coast are protected by breakwaters.
Lake Michigan.—The area of Lake Michigan includes Green Bay on the northwestern shore, and Grand Travers Bay directly on the eastern shore. Many islands lie in the lake between these two breaks in the shore, which elsewhere is low and unbroken.
About the southern and eastern borders are immense heaps of sand which have been piled up by waves and currents, and drift inland by the winds, sometimes, as at Sleeping Bear bluffs, completely burying the heavy forests.
The level of Michigan varies, but not as greatly as does that of Huron, according to the direction and force of the winds, the changes in rainfall, evaporation, atmospheric pressure, etc. Except when caused by protracted gales blowing steadily in one direction, this variation rarely exceeds one and three-tenths feet. The lake has a lunar tide with accompanying variation of from one and one-half inches neap to about three inches spring tide, and the water is warmer than the air in winter and cooler in summer, and visibly ameliorates the climate of the shores, as may be shown in the quantity and rich quality of the Michigan fruits. Like all the Great Lakes, Michigan abounds in fish, such as whitefish and trout.
Lake Erie has a northeast and southwest direction, bounded on the entire upper shore by the Province of Ontario, and on the southern and eastern shores by Ohio, Pennsylvania and New York. At its southwestern end it is connected with Lake St. Clair by the Detroit River. At its northwestern end it discharges into Lake Ontario through the Niagara River. It is connected by the Welland Canal with Lake Ontario and by other canals with the Hudson and Ohio Rivers, making it thus a link in the waterway from east to west.
Besides the drainage from the Lake Superior system, Lake Erie receives the Grand River, the Maumee from the west, and the Sandusky and Cuyahoga from the south. The west coast is broken by the islands of Put-in-Bay.
Lake Ontario is the most eastern, with a northeast and southwest direction, like Lake Erie. It is the lowest of the Great Lakes, and has naturally the largest discharge, three hundred thousand cubic feet per second. The shores are flat, except in the Bay of Quinte, which extends on the northeast fifty miles inland. There are many harbors and flourishing ports. The waters have a surface current, due to the fact that the larger axis of the lake coincides with the direction of the prevailing westerly winds. This, added to frequent violent storms, keeps the lake from freezing, except a few miles in width along the shores.
Lake Ontario is connected with the Erie Canal and Hudson River by the Oswego Canal and with the Ottawa River by the Rideau Canal.