Sand and swamp vegetation.—While almost all of Illinois was originally covered by forests and upland prairies, there were regions of sand and swamp which had their characteristic vegetation. Much of the sand areas have been brought under cultivation, but thousands of acres still exist in their original condition. The bunch-grass association of plants originally occupied more than nine-tenths of the unforested portion of the sand area. The bunch-grass formation extended over hill and dale except where interrupted by "blowouts," areas of bare sand where depressions have been formed by wind action. The principal vegetation of these "sand prairies" consists of ten species of bunch-grass, the bunches of the various species vary ing from four inches to three feet in diameter.
The principal sand areas are in the northern half of the state and on the flood plains on the cast sides of rivers. The Havana area extends from Pekin in Tazewell County to Mere dosia in Morgan County, a distance of 75 miles. The plain reaches a width of 14 miles in Mason County. While the sand
deposits occupy only a portion of the area, their aggregate extent is estimated at 179,000 acres. The Hanover area of nearly 6,000 acres lies in the second bottoms of the Mississippi Valley in Jo Daviess County. The Oquawka area is along the Mississippi in Henderson and Mercer counties; the Amboy area along Green River in Lee County. The Kankakee area of 3,000 square miles lies mainly in Indiana; about one-fourth is in Iroquois and Kankakee counties of Illinois.
Extensive areas of the upland prairies were swamp lands occupied by vegetation appropriate to the natural conditions. These upland swamps have been so fully drained and culti vated that their natural vegetation has disappeared almost as completely as that of the typical well-drained prairies. Skokie Marsh in Lake and Cook counties still exhibits much of its natural vegetation. This marsh is about S miles long and 1 mile wide and contains a native flora of 217 species.