Part 1

Educational Series 9

INSIDE ILLINOIS Mineral Resources

Illinois State Geological Survey

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).

DRIFTLESS AREA WISCONSINAN MORAINES ILLINOIAN TILL PLAIN MISSISSIPPI RIVER WABASH RIVER SHAWNEE HILLS OHIO RIVER

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?

The mantle, which surrounds the core, is a rigid zone of materials rich in iron and magnesium. These materials are not as dense as those found in the core.

WHAT IS THE CRUST OF THE EARTH AND HOW IS IT DISTINGUISHED FROM THE MANTLE AND THE CORE?

The crust, the top part of which includes the ground we walk on, is the hard, outer surface layer of the earth. Although the crust is about 6 to 30 miles deep, the scale (size) of figure 2 allows it to be drawn only as the thin outer line. The rocks and minerals that we are all acquainted with are found in the crust. These rocks are not as dense and do not have as high an iron content as do the rocks of the mantle and the core.

WHAT IS THE EARTH’S CRUST UNDER ILLINOIS MADE OF?

The earth’s crust under Illinois is made of: sedimentary rocks deposited by water, wind, or glaciers (limestone, sandstone, shale, glacial drift); igneous, or melted rocks (granite, gabbro); and metamorphic, or altered sedimentary and igneous rocks (quartzite, gneiss). These various types of rocks have a relatively thin covering of broken or weathered material called mantle rock and soil.

WHEN AND HOW WAS THE LAND SURFACE OF ILLINOIS FORMED?

The ground surface over most of Illinois was formed during the ice age (Quaternary Period) which lasted from about one million years ago up to nearly 5,000 years ago. As much as 90 percent of the state was covered by one of several sheets of glacial ice (fig. 3). The glaciers smoothed down and covered much of the old, rocky, hilly land surface and filled old valleys with loose, unconsolidated deposits.

WHERE DID THE LOOSE, UNCONSOLIDATED DEPOSITS COME FROM AND WHAT ARE THEY MADE OF?