What is the design of a protective tariff? What are its advantages and disadvantages? Why are most of the great steel-making plants so remote from the mines of iron ore used in making steel? FOR COLLATERAL READING Industrial Evolution of the United States--Chapters III-V. Mineral Resources of the United States. Outlines of Political Science--Chapters VIII-X. CHAPTER XIX THE UNITED STATES--THE BASIN OF THE GREAT LAKES AND THE MISSISSIPPI VALLEY The principal agricultural region of the United States extends from the Appalachian ranges to the Rocky Mountains. A certain amount of bread-stuffs, meat, and dairy products are grown in nearly every part of the country for local use, but the grain, meat, and cotton of this region are designed for export, and are therefore factors in the world's commerce. The basin of the Great Lakes connects the Mississippi Valley with the Atlantic seaboard. =The Basin of the Great Lakes.=--This region includes not only the Great Lakes and the area drained by the streams flowing into them, but also a considerable region surrounding that commercially is tributary to the traffic passing over the lakes. This basin itself is a part of a trade-route destined very shortly to become one of the greatest highways of traffic in the world. The lakes afford a navigable water-way which, measured due east and west, aggregates nearly six hundred miles. This route is interrupted at Niagara Falls and at St. Mary's Falls, between Lake Superior and Lake Huron. On the Canadian side, Welland Canal, Lake Ontario, and the St. Lawrence connect Lake Erie with tide-water. In the United States the Erie Canal connects the lake with the Hudson River and New York Bay. From the head of Lake Superior railway routes of minimum grades--the Great Northern and the Northern Pacific[51]--cross the continent to Puget Sound, the best harbor approach to the Pacific coast of the American continent. The harbors of Puget Sound, moreover, are materially nearer the great Asian ports than any other port of the United States. The level margins of these lakes are roadbeds for many miles of railway track; in many instances the railways are built on the tops of terraces that once were shores of the lakes. [Illustration: DULUTH] _Duluth_, at the head of Lake Superior, became commercially important when the St. Mary's Falls Canal was completed. Much of the tremendous tonnage of freight passing through the canal is assembled at this place. The freight shipped consists mainly of farm products collected from an area reaching as far west as the Rocky Mountains. There is also a considerable shipment of iron ores obtained near by. _Buffalo_, at the lower end of Lake Erie, owes its activity to the trade in lumber, grain, and other farm products that come from Western lake-ports. It is the eastern terminus of the lake-commerce and the western terminus of the Erie Canal.