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The Basin of the St Lawrence and the Great Lakes 319

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THE BASIN OF THE ST. LAWRENCE AND THE GREAT LAKES 319. A long trade route region.—It is a long way from Duluth and Chicago past Detroit, Montreal, and Quebec to the lower end of the Gulf of St. Lawrence; but all parts of the region are much alike in their great dependence on trade, and also in their climate and agriculture.

What regions bound the St. Lawrence Valley and the Lower Lake District? All of this region is lowland, except the north western part, which we call the Upper Lake District.

320. The effects of the Great Glacier.—The Great Lakes form the largest group of lakes in the world. Lake Superior is the largest body of fresh water in the world. These lakes were made by the great ice mass that once pushed its way southward over this part of North America. The moving mass of ice scooped out great, deep holes (Fig. 262). The from the holes, car ried along by the ice, dammed up the old channels of streams (Sec. 314). When the glacier filled up the St. Lawrence Valley, the waters from the melting ice formed a large lake in front of the glacier. The mud and sand deposited on the bottoms of these old lakes now make fine agricultural soils along the south shores of Lakes Ontario, Erie, and Michigan.

As the ice front changed, the water found different outlets. At one time the waters of Lake Superior flowed south into the Mississippi at a point north of St. Paul. The waters of Lake Michigan flowed down the Illinois River into the Mississippi. Lake Erie waters flowed to the Ohio River. Later, ' as the glacier melted still more, Lake Erie waters flowed across New York by way of the Mohawk, and finally they found still another new channel by tumbling over a ledge of rock into Lake Ontario. The swiftly flowing stream cut the edge of the ledge, and gradually wore the rock away, until to-day the falls are at Niagara instead of at Lake Ontario. Measure on the map (Fig. 204) the length of the river channel below Niag ara Falls. See in Fig. 262 how great the dif ference in level is between Lake Erie and Lake Ontario.

The Niagara River is a very young river flowing through a narrow gorge. (Figs. 142, 146, 147.) Niagara Falls, one of the won ders of the earth, is visited by thousands of tourists from all parts of the world. Niagara

Falls is to-day developing more hydroelectric power than any other waterfall. (Fig. 261.) In this region the glacier has (a) helped man to trade by making waterways; (b) put men into factories by giving them water power; (c) made farming easier by making smooth plains on old lake beds; (d) made farming harder than in some other regions because it left much of the region rolling and hilly and dotted with many small lakes. For this rea son, a hundred-acre farm near the Great Lakes or ' along the St. Lawrence may have some fields that are too hilly or stony or swampy to plow.

321. Transportation and cities.—Because the Great Lakes and the St. Lawrence River provide a trade route, trading and manufacturing industries have been devel oped until they support more people than do the farms. In this region the lake steamers have caused many cities to grow. It is a curious thing, this lake steamer. It is like a great iron box with a flat bottom. (Fig. 281.) It has a little house in one end full of ma chinery, and another little house in the other end where the crew live. There are hundreds of these black, smoking freight boxes, which are really floating warehouses. Many of them carry 10,000 tons of freight from the far ends of Lake Superior or Michigan to the lower end of Lake Erie. The Welland Canal, by way of which boats go from Lake Erie to Lake Ontario, is large enough to allow only boats of 2,500-ton capacity to pass through, but there are plans for enlarging it. When it has been improved, the eargoes of the large boats will not have to be unloaded at one end of the canal and reloaded, but will pass directly through the canal in the big ships to their destinations. Look at the New York Barge Canal (Fig. 204) and explain how the Great Lakes route has two sea ends, and why Montreal and Quebec are important commercial cities. The great drawback to the route is that the river and all the canals are frozen for several months each winter. Fortunately the seaports are not frozen more than a day or two at a time.

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