Lake Superior is fairly well provided with natural harbours, and works of improvement have created additional har bours of refuge at various points. Marquette, Mich., Presque Isle Point, Mich., Agate Bay, Minn., Grand Marais, Minn., and Ash land, Wis., are on bays which have protective breakwaters across their mouths. Duluth, Superior, Port Wing, Wis., Ontonagon, Mich. and Grand Marais, Mich., are harbours with entrances formed by parallel jetties extending across obstructing bars. On the Canadian side Fort William, in the mouth of the Kaminis tikwia, and Port Arthur, 4 m. distant, an artificial harbour, are the only important shipping points, being the lake terminals of two great trans-continental railway systems, though the whole north shore is liberally supplied with natural harbours.
The traffic on Lake Superior grows constantly in volume. The data collected at United States and Canadian locks at the Sault was as follows in 1927: passengers 55,115; coal 17, 107,500 tons; flour 938,344 tons; wheat
tons; other grain 2,948,295 tons; iron ore 50,098,068 tons; miscellaneous 2,334,912 tons. The total traffic was 83,354,064 tons, valued at
over $1,000,000,000. The increase in the past 20 years has been about 00% in both tonnage and value. The principal freight shipped eastward consists of flour, wheat and other grains, through Duluth-Superior from the United States, and through Fort Wil liam-Port Arthur from the Canadian prairies; copper ore from the mines on the south shore; iron ore in immense quantities from both shores, the principal ore-shipping ports being Ashland, Two Harbors, Marquette and Superior, and lumber produced on the tributary rivers. West-bound freight consists largely of coal for general distribution and for terminal railway points.
BiBuoGRAPHY.—Bulletin No. 37, Survey of Northern and North western Lakes, Lake Survey Office, Detroit (April 1928) ; Transporta tion on the Great Lakes, Government Printing Office (1926) ; Annual Report of the chief of engineers, U.S. army, Government Printing Office (1926) ; House Document No. 253, loth Congress, ist Session, Government Printing Office (1928).