Lake Michigan

MICHIGAN, LAKE, the third largest of the Great Lakes of North America and the only one wholly within the boundaries of the United States. It is about 307 m. in length, averages about 7o m. in width, and has a maximum measured depth of 870 feet. The lake is bounded on the north and east by the State of Michi gan, on the south by Indiana and on the west by Illinois and Wis consin. It has a water surface of 22,400 sq. m. and a drainage basin of some 69,040 sq. miles. Taking the average for the past 68 years, its mean surface is 580.94 ft. above mean sea-level, being the same as Lake Huron and 21.28 ft. below that of Lake Superior. The average or normal elevation of the lake surface varies irregularly from year to year. During the course of each year, the surface is subject to a consistent seasonal rise and fall, the lowest stages prevailing during the winter months and the highest during the summer months. In addition to the annual fluctuation, there are occasional oscillations of irregular amount and duration. Sometimes these are apparently seiches, resulting from variations in barometric pressure, which may produce changes ranging from a few inches to several feet, and return to normal, within a few hours. The dangerous storms of the au tumn, winter and early spring are usually westerly. Ice interferes with navigation in the northern part of the lake in winter; the average closing and opening dates for navigation in the Straits of Mackinac are Dec. 15 and April 12, respectively.

Harbours.---The

harbours along the shores are generally situ ated at the mouths of rivers. Most of these rivers are small and unimportant, the larger streams being the Menominee and the Fox, both of which empty into Green bay, the most important arm of the lake. The early plan of improvement consisted of parallel piers protecting a dredged channel; subsequently, at some harbours, detached breakwaters were built to provide addi tional protection from prevailing storms. In recent years, the in jurious effects of storm waves in inner harbours have been re lieved by the formation in the lake of a wave-stilling basin, enclosed by breakwaters or piers which converge to an entrance opening in deep water beyond the inner piers, this basin allow ing the waves to expand and lose force instead of being conducted through the confined channel between the parallel piers. Such

basins now exist at Holland, Ludington, Manistee, Manistique, Two Rivers, Manitowoc, Sheboygan and Racine. The outer har bours at Milwaukee, Chicago and South Chicago (Calumet), pro tected by breakwaters, afford commodious and safe anchorage for all classes of vessels. The harbours of Port Washington, Waukegan, Indiana Harbor and Gary are entirely artificial, consisting of dredged channels and basins protected by breakwaters and piers. As a result of the improvements made and maintained by the United States and local interests, the harbours are generally accessible to vessels drawing from 14 to 21 ft. at low stages.

The port of Escanaba on the north shore of the lake is an im portant shipping point for iron ore. Green Bay and Milwaukee are centres of distribution for coal from Lake Erie ports. Near the south end of the lake the Chicago district is a great industrial centre, consuming large quantities of water-borne raw materials, principally iron ore, coal and limestone, which are handled through the important ports of Calumet (South Chicago), Indiana Harbor, Gary and Buffington. Milwaukee, Chicago and Calumet are grain shipping ports.

The commerce for the calendar year 1927 of the principal ports on the lake in tons is shown in the following table:— Commerce of Ports on Lake Michigan During 1927 The transfer of loaded freight cars on car ferries on the Great Lakes was inaugurated in 1892 by the Ann Arbor railroad. The present service on Lake Michigan, which is by far the most ex tensive of its kind in the world, consists of two ferries operated between Grand Haven, Mich., and Milwaukee, Wis., by the Grand Trunk railway; seven between Ludington, Mich., and Milwaukee, Manitowoc, Wis., and Kewaunee, by the Pere Marquette railway; four between Frankfort and Menominee and Manistique, Mich., and between Frankfort, Mich., and Manitowoc and Kewaunee, Wis., by the Ann Arbor railroad.