2. The Bloomington moraine consists at places of a single ridge, at other places of a group of ridges extending from Indiana across Illinois to Peoria County, where it overlaps the Shelbyville moraine and continues at the outer margin of the Early Wisconsin glaciation to Kane County, where it, in turn, is overlapped by the Late Wisconsin.
3. The Valparaiso moraine belongs to the Late Wisconsin glaciation. It is a broad belt of massive ridges extending from Grand River in Michigan across northwestern Indiana, northeastern Illinois, and along eastern Wisconsin to Green Bay.
Other minor moraines are conspicuous features of the land scape, and a number have been named from cities located on them. Thus we have: (1) the Champaign moraine with its offshoot, the Cerro Gordo moraine; (2) the Chatsworth ridge and the Cropsey ridge branching from the Bloomington moraine; (f) the Marseilles moraine crossing the Illinois River at Marseilles; (4) the Minooka ridge extending from the Valparaiso moraine along the county line of Kendall and Wi11 counties.
On the map, all moraines of the Early 'Wisconsin are repre sented by No. 9 and those of the Late Wisconsin by No. 10.
While the terminal moraines of the Wisconsin drift stand out conspicuously in the landscape, the larger area of the Wisconsin glaciation belongs to the level "ground moraines" occupying the broad stretches between the ridges of the terminal moraines. They form extensive areas of fertile farm land of sufficient slope to be easily drained, and sufficiently level to reduce loss of fertility by erosion to a minimum and to make the operation of modern farm machinery easy and highly profitable. The ground moraines of the Early Wisconsin, No. 11 on the map, are much more extensive in Illinois than those of the Late Wisconsin (No. 12).
Sand, swamp, and bottom lands.—During and after the retreat of the ice sheets from Illinois, great streams of water flowed across the state, the water supply coming from the rainfall and from the melting glacier. While the massive ice sheet blocked the outlets to the east and northeast, glacial lakes formed along the front of the ice harrier, the ice forming their northern shores and the terminal moraines their southern margins.
Large areas of north eastern Illinois in the Wisconsin glaciation were thus regions of shal low lakes. Much of the
land of this region today consists of the basins of these lakes drained by the withdrawal of the glacial barrier, or by clown-cutting of their outlets, or by great open ditches constructed by man.
The most noted of these glacial lakes in Illinois is known as Lake Chicago, the ancestor of Lake Michigan. As the glacial barrier prevented the flow of water along its present outlet, the waters of Lake Chicago, bordered by the ice on the north and by the massive Valparaiso moraine on the south, rose until they found an outlet across the Valparaiso moraine along the present drainage line of the Des Plaines River. The broad, deep valley, eroded by the escaping waters of Lake Chicago, is known as the "Chicago Outlet." The valley bluffs of the Chicago Outlet are conspicuous and interesting features of the landscape to the traveler between Chicago and Joliet. The Chicago Outlet furnished easy portage to Joliet and Marquette in 1673, and later to La Salle and other explorers. It became the route, successively, of the Illinois and Michigan Canal; the Santa Fe and the Chicago and Alton railroads; the Chicago Drainage Canal; and the Chicago and Joliet electric railroad.
The "Chicago Plain," the bottom of Lake Chicago which has been made dry land by the withdrawal of glacial waters, covers much of Cook County and extends into Indiana.
Sediment in great quantities was carried by the streams flowing across Illinois from the retreating Wisconsin glacial lobe. This sediment was deposited in the shallow glacial lakes and on the flood plains of the streams. The valleys were so well filled by the excessive water supply, and the sediment was so abundant, that the bottom lands developed along these streams during earlier stages of glaciation were widely and deeply covered by the sediments of the drainage waters of the Wisconsin stage. Where sand was abundant, the winds carried it beyond the immediate limits of the valley, thus forming considerable areas of sand deposits especially in Mason, Tazewell, and other river counties. These sand areas are mainly east of the Illinois River, due to the strength of the prevailing 1\ esterly winds.