The basins of the Iroquois and Kankakee proper are separated by an arm of the Valparaiso moraine. The Kan kakee is separated from the Lake Michigan and Des Plaines basins by the broad, bulky, and rugged ridges of the main body of the Valparaiso moraine which rises to a height of 200 feet or more above the flat lands to the south and west.
The Des Plaines River flows along the eastern edge, and Fox River flows along the western edge, of the Wisconsin arm of the Illinois River Basin, within the broad belt of the Val paraiso moraine. The Des Plaines breaks across the moraine along the Chicago Outlet, and the Fox works its way to the western edge of the moraine near Aurora. The surface forma tions of this region are in striking contrast to those of the main part of the Kankakee Basin. The chief topographic feature is the Valparaiso moraine whose broad north-south ridges, separated by stream valleys or by more level areas of glacial till, occupy a width of more than 20 miles, and rise to a height of 300 feet above Lake Michigan.
The only important lake district of Illinois lies in the Valparaiso moraine of Lake County where the typical irregulari ties of morainal topography furnish numerous small basins which contain bodies of water varying in size from mere ponds to several square miles in extent. Good railroad service and excellent automobile routes between Chicago and this region are leading to development ,of summer resorts and summer homes on the shores of many of the lakes.
For a distance of 27S miles from the confluence of the Des Plaines and the Kankakee, the Illinois River trenches its basin somewhat to the north and west of a middle line. The most conspicuous topographic feature of the basin is the valley itself, having a width varying from 1 to 15 miles, bordered by valley sides varying in height from low ridges to precipitous or sloping bluffs rising 100, 200, or even 300 feet above the valley floor. The long stretches of the Illinois Valley not spanned by wagon bridge or railroad bridge indicate the strong control of this important valley on transportation routes. Wagon bridges have been built only where they give direct approach to a city of some importance. The only wagon bridges across the 215 miles of the valley below the Great Bend are at Chillicothe, Peoria, Pekin, Havana, and Beardstown. Ferryboats still operate at many inter vening points. Railroad bridges are more numerous than wagon bridges.
The flood plain of the Illinois Valley contains large areas of swamp lands, some of which have been reclaimed by levees built at great expense. As land values increase, additional
portions will doubtless be drained. Numerous lakes, portions of former river courses, are found on the flood plain, and in many instances they yield a fish product as valuable as the farm products from an equal area of good agricultural land.
The tributary valleys of the Illinois and their numerous subdivisions form a network of valleys throughout the entire basin, and everywhere they are important topographic features of the landscape. They furnish necessary drain age lines; contain in most cases a fertile soil; suffer occasionally from high water; and require large expenditures for highway and railroad crossings. The traveler who under stands the development and significance of stream valleys will find much to interest and to instruct him as he journeys across Illinois whether by rail road or motor car.
Next to the stream valleys, the most conspicuous topo graphic features within the Illinois Basin are the various glacial moraines. These ridges of glacial drift lend variety to an other wise flat landscape. The Illinois Basin contains large portions of all the important systems of glacial moraines in the state— Illinoisan, EarlyWisconsin, and Late Wisconsin—Nos. 2, 9, and 10 of the soil map (facing p. 152). These terminal moraines rise in ridges of gentle or even rugged topography above the more level ground moraines on either side. They are usually distinct and easily traced by the observer. They may appear as low mounds; as short narrow ridges either single or branch ing; or they may be hundreds of miles in length, 10 to 20 miles in width, and 200 feet or more above the level ground moraine. With the soil map for reference, the traveler may sec and understand these ridges and their significance even when traveling rapidly through the state. The Illinois Basin as a whole is a region of rather flat land, but the slope is everywhere sufficient to insure good drainage except in the flood plains of the main valley and some of its tributaries. Its area of 2S,000 square miles is divided among three states as follows: Illinois contains 24,000 square miles; Indiana 3,000 square miles; and Wisconsin 1,000 square miles. The basin forms an extensive area of extremely fertile agricultural land which, under the Illinois system of scientific agriculture, is destined to remain one of the great food-producing regions of the world.