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-_ THOMPSON'S COAST PILOT. a much more favorable cause than the small depth of its water, which may be far more appropriately adduced as the reason why the navi- gation is obstructed by ice much more than either of the other great lakes. 2 The ascertained temperature in the middle of Lake Hrie, August, 1845, was temperature of air 76° Fahrenheit, at noon-- water at surface 73°--at bottom 53°. Lax Onranro, the fifth and last of the Great Lakes of Amer- ica, is elevated 234 feet above tide-water at Three Rivers, on the St. Lawrence ; it is 180 miles long, 60 miles broad, 600 feet deep. Thus dasin succeeds basin, like the locks of a great canal, the . whole length of waters from Lake Superior to the Gulf of St. Law- rence being rendered navigable for vessels of a large class by means of the Welland and St. Lawrence Canals--thus enabling a loaded vessel to ascend or descend 600 feet above the level of the ocean, or tide-water. Of these five great lakes, Lake Superior has by far the largest area, and Lake Ontario has the least, having a surface only of about one-fifth of that of Lake Superior, and being somewhat less in area than Lake Hrie, although not much less, if any, in the circuit of its shores. Lake Ontario is the safest body of water for navigation, and Lake Erie the most dangerous. 'The lakes of great- est interest to the tourist or scientific traveler are Ontario, Huron, together with Georgian Bay and North Channel, and Lake Superior. The many picturesque islands and headlands, together with the pure, dark, green waters of the Upper Lakes, form 'a most lovely contrast during the summer and autumn months. The altitude of the land which forms the water-shed of the Up- per Lakes does not exceed from 600 to 2,500 feet above the level of _the ocean, while the altitude of the land which forms the water-shed of Lake Champlain and the lower tributaries of the St. Lawrence River rises from 4,000 to 5,000 feet above the level of the'sea or tide-water, in the States of Vermont and New York. The divide which separates the waters of the Gulf of Mexi¢o, from those flowing northeast into the St. Lawrence, do not in some places exceed ten or twenty feet ahove the level of Lakes Michigan and Superior ; in fact, it is said that Lake Michigan, when under the influence of high water and a strong northerly wind, discharges