portions of Illinois valuable deposits of lead occur under conditions similar to those associated with the lead and zinc mines about the northern border of the Ozark uplift. Owing to the demand for transportation facilities and the mild relief of the land, the entire extent of the Prairie plains is covered with a double-lined network of steel. The ganglia in this pulsating nerve system of intercommunication are Chicago (here included, as it belongs to the prairie as well as to the Great Lakes region), St. Louis, Kansas City, Omaha, Minneapolis, St. Paul, etc., cities with from 100,000 to over 1,500,000 inhabitants, and hundreds of lesser centres of trade, manufacture, and education. _The Lake Plains._--The region draining to the Great Lakes--or the Laurentian lakes, as they may, perhaps, be more properly designated, since they form the source of the river of that name--presents many striking contrasts to the more monotonous treeless prairies skirting it on the south and west. The name "Lake plains," suggested by J. W. Powell for the portion of the region here referred to within the borders of the United States, when extended to the entire area draining to the Laurentian lakes, is in part a misnomer, since much of its surface is rough and irregular. In a certain sense, however, the term _plain_ is applicable, since it includes a plain of water over 95,000 square miles in area. The combined areas of the lakes are greater than that of the region draining to them. The land bordering the Laurentian lakes is underlaid to a large extent by horizontal or but slightly disturbed sedimentary rocks, but includes on the north a portion of the contorted, crystalline terranes already referred to as forming the Laurentian Highlands, and in general is characterized by the mildness of its relief. The elevations of the surfaces of the several Laurentian lakes above the sea are, in feet, as follows: Superior, 602; Michigan and Huron, 582; Erie, 373; and Ontario, 247. The land forming the margins of these water bodies rises in general less than 300 feet above their surfaces. In portions of northern Michigan and in the region of crystalline rocks to the north of Lakes Superior and Huron, however, the relief is more pronounced and there are many bold rounded hills with basins between them. The principal part of the nearly plane land surface about the Laurentian lakes is in immediate proximity to their borders, and records the former extent of their waters. These plains, composed of clay deposited from the lakes when more widely expanded than at present, form a fringe from 5 to 50 or more miles broad all about the present lake margins. Across this gently sloping surface the streams from the uplands, increasing in length as the lakes were lowered, have excavated narrow, steep-sided channels. These modern plains furnish typical illustrations of young topography.