Educational Series 9 _INSIDE ILLINOIS Mineral Resources_ _Illinois State Geological Survey_ [Illustration: SEAL OF THE STATE OF ILLINOIS • AUG. 26^TH 1818] STATE of ILLINOIS DEPARTMENT of REGISTRATION and EDUCATION 1965 ILLINOIS STATE GEOLOGICAL SURVEY John C. Frye, Chief URBANA, ILLINOIS Printed by Authority of State of Illinois, Ch. 127, IRS, Par. 58.25. INSIDE ILLINOIS— _Mineral Resources_ Although Illinois has been nicknamed the “Prairie State,” many parts of it are hilly and scenic. The idea of large areas of the state being nothing more than broad, flat prairies has come about because the major highways have been built to take advantage of the comparatively low, gently rolling landscape rather than the rougher more scenic areas. Physiography is the study of the creation and gradual change of land surface forms (the landscape). Thus, the land surface as we see it today in each of the physiographic provinces (fig. 1) has had a particular history of development. Illinois is about 385 miles long from north to south and about 218 miles wide. It has an area of 55,947 square miles. The average elevation of the state is about 600 feet above sea level. Charles Mound, however, in the northern part of Jo Daviess County in extreme northwestern Illinois, has an elevation of 1,241 feet above sea level and is the highest point in the state. Cheap water transportation is available to Illinois industry through Lake Michigan, the Illinois Waterway, and the Mississippi, Ohio, and Wabash Rivers. These major rivers of Illinois collect the surface drainage of the state from a network of about 500 streams. WHAT IS THE EARTH MADE OF BENEATH THE GROUND SURFACE? The earth is made of a large number of different rocks and minerals (limestone, sandstone, shale, coal, iron, granite, and many others). These materials are divided into three zones: core, mantle, and crust (fig. 2). [Illustration: Figure 1—Physiographic provinces of Illinois.] DRIFTLESS AREA WISCONSINAN MORAINES ILLINOIAN TILL PLAIN MISSISSIPPI RIVER WABASH RIVER SHAWNEE HILLS OHIO RIVER [Illustration: Figure 2—The earth with a segment removed to show supposed internal zones.] Crust (6-30 miles) Mantle (1800 miles) Outer core (1400 miles) Inner core (750 miles) WHAT IS CORE? The core is the innermost zone of the earth. It is mainly iron with some nickel and cobalt. The inner core probably is solid, but the outer core may consist of the same elements in a molten form. The core is the most dense (heaviest) of the three zones. HOW DOES THE MANTLE DIFFER FROM THE CORE?