The great lakes in Canada give a character to that country distinct from any other in the Old World or the New. They are very numerous; some far exceed all inland waters elsewhere in depth and extent; they feed, without apparent diminution, the great river St. Lawrence; the tempest plows their surface into billows that rival those of the Atlantic,[118] and they contain more than half of all the fresh water upon the surface of the globe.[119] Superior[120] is the largest and most elevated of these lakes: it is crescent-shaped, convex to the north; to the southeast and southwest its extremities are narrow points: the length through the curve is 360 geographical miles, the breadth in the widest part 140, the circumference 1500. The surface of this vast sheet of fresh water is 627 feet above the level of the Atlantic; from various indications upon the shores, there is good reason to conclude that at some remote period it was forty or fifty feet higher. The depth of Lake Superior varies much in different parts, but is generally very great; at the deepest it is probably 1200 feet. The waters are miraculously pure and transparent; many fathoms down, the eye can distinctly trace the rock and shingle of the bottom, and follow the quick movements of the numerous and beautiful fish inhabiting these crystal depths. No tides vary the stillness of this inland sea, but when a strong prevailing wind sweeps over the surface, the waves are lashed to fury, and the waters, driven by its force, crowd up against the leeward shore. When in the spring the warm sun melts the mountain snows, and each little tributary becomes an impetuous torrent pouring into this great basin, the level of the surface rises many feet. Although no river of any magnitude helps to supply Lake Superior, a vast number of small streams fall in from among clefts and glens along the rugged shores;[121] there are also many large islands; one, Isle Royale, is more than forty miles in length. In some places lofty hills[122] rise abruptly from the water's edge; in others there are intervals of lower lands for sixty or seventy miles, but every where stands the primeval forest, clothing height and hollow alike. At the south-eastern extremity of this lake, St. Mary's Channel carries the superabundant waters for nearly forty miles, till they fall into Lake Huron; about midway between, they rush tumultuously down a steep descent, with a tremendous roar, through shattered masses of rock, filling the pure air above with clouds of snowy foam.