A study of the map reveals the relation of the old bottom lands and the late bottom lands to each other, to the stream valleys, and to the shallow glacial lakes. No. 13 represents the "old river bottom and swamp areas." It is found outside the Wisconsin glaciation along the streams in the Illinoisan glaciation, often separated from the stream by No. 14 repre senting "sand, late swamp, and bottom lands." Before the Wisconsin stage, these flood plains were wholly occupied by No. 13, the "old river bottom and swamp areas." The flood of waters from the Wisconsin glacier with its load of sediment very largely buried these "old river bottom and swamp areas" beneath the materials represented by No. 14 as the "sand, late swamp, and bottom lands." Interesting relationships between these old and late river bottoms appear from a study of the map along the Illinois River, along the Mississippi and its tributaries in southern Illinois, and especially along the Wabash and its Illinois tributaries, the Embarras, Little Wabash and its Skillet Fork, and along the Saline River and its tributaries.
Results of glaciation.—No event of geologic history means as much to Illinois as the activities of the North American ice sheet. The fertile soils formed during the Glacial period
are of greater value to the citizens of Illinois than the great wealth of the coal de posits of the Pennsyl vanian period. Illinois was so fortunately situ ated that the rock ma terial entering into her glacial soils was such as to furnish necessary plant food in abundance, thus producing a soil which, with scientific treatment, will maintain its fertility through an indefinite fu ture. In the glacial drift are found deposits of sand, gravel, and clay, valuable for building purposes, for drainage tile, pottery, and road-making materials. The level surface of the glaciated regions of the state have invited railroad building which gives all parts of Illinois splendid transpor tation facilities. Although Illinois stands twenty-third in area, the fact that she stands first in value of farm lands and farm crops, second in railroad mileage and wealth, and third in population and manufactures, is due very largely to the extensive and thorough work of the ancient ice sheet within the state.