St. Lawrence, a great river of North America which flows about 750 miles N.E. from Lake Ontario to the Gulf of St. Lawrence. In a wider sense the name embraces the whole chain of great lakes (Superior, Michigan, Huron, Erie, Ontario), with the rivers between them up to the river St. Louis in Minnesota, the ultimate source of this enormous mass of fresh water, which has a drainage basin of 297,600 square miles. For nearly half its course the St. Lawrence varies in width from 1 mile or under to 3 or 4 miles, but about 400 miles above the Gulf it begins to expand into a broad estuary the distance between the banks at the mouth being over 100 miles. Some of the broader parts of the upper river are studded with numerous islands, and a long stretch immediately below Lake Ontario, called the Lake of the Thousand Isles is famous for its beautiful scenery. The channel was widened and deepened in 1858, so as to afford access for vessels of 4,000 tons to Montreal, 600 miles above the mouth. The chief tributaries are the Ottawa and the Richelieu. The GULF OF ST. LAWRENCE, into which the river flows, lies between Labrador on the N., Lower Canada on the W., New Brunswick on the S.W., Nova Scotia and Cape Breton Island on the S., and Newfoundland on the E. Its length from N. to S. is about 300 miles, and its breadth about 240 miles.