“ The Mississippian rocks are a source of limestone, fluorspar, zinc, and ganister, and are of greatest economic significance in southeastern Illinois where they are the most important of our oil-producing rocks. ”

“ During the Ice Age, most of Illinois was repeatedly invaded by huge glaciers, sometimes towering a mile or more high, that carried embedded in them ground up rock materials they had gouged out of the bedrock to the north as they ponderously pushed south. ”

“ Minerals produced commercially in Illinois include crude oil, coal, limestone, dolomite, clay, sand, gravel, fluorspar, tripoli, ganister, novaculite gravel, silica sand, and the metals zinc and lead. The distribution of mineral industries, shown in the several maps of figures 8 through 12, is, of course, related to the distribution of the rocks (plate 1) . For example, the coal mines are scattered along the margin of the area of Pennsylvanian rocks where the coals are at relatively shallow depths. ”

“ In extreme southern Illinois and in north-central Illinois, the rock layers are broken by great faults (see figures 5 and 6) which displace the layers of rocks by as little as a few inches to as much as 3,000 feet.
The structural map of Illinois (figure 6) shows the position of the major geologic structures. The big basin is indicated by shading, with the darkest pattern showing where the basin is deepest. The same strata that lie at sea level at the basin’s outer edge are downwarped to 6,000 feet below sea level in its deepest part. ”

“ Between 1820 and 1865, the mining area of which northwestern Illinois is a part was the nation’s principal producer of lead ore. In recent years production of zinc has increased and that of lead has decreased. ”

“ Illinois ranks fourth in the nation among states that produce bituminous coal, the type of coal most widely mined in the United States. Coal is used by many manufacturing industries, by public utilities companies that burn coal to generate electricity, and by individuals for heating homes.
All Illinois coal deposits are found in the Pennsylvanian System. Of the many coals, only a few are thick enough to be mined profitably. The coal is of bituminous rank, but it varies in quality. ”

“ In the Illinois Basin all these formations are overlain by Pennsylvanian rocks which offer only small, scattered supplies of ground water.
ILLINOIS STATE GEOLOGICAL SURVEY
A city or farmer needs a new water supply. Where can suitable water-bearing formations be found? A new limestone quarry is considered. Where are the most suitable limestone deposits? A coal mine is being planned. How deep must a shaft be sunk to reach the nearest minable coal and what will the mining conditions be? A land owner has a clay deposit on his land. What uses can be made of it? A road is to be constructed. ”

“ Figure 1—A mantle of glacial drift covers the bedrock in much of Illinois.
WISCONSINAN GLACIAL DRIFT KANSAN GLACIAL DRIFT ILLINOIAN GLACIAL DRIFT
The glacial drift belongs to the youngest (topmost layer) of the major divisions of our rocks, which geologists have named the Pleistocene (scientific name for Ice Age deposits) .
Most of the drift is an unsorted mixture of clay, pebbles, and boulders called “till,” but some glacial deposits consist of water-sorted sand and gravel carried and deposited by meltwater from the glaciers. ”

“ Lead and zinc are the only metallic minerals mined in Illinois. Deposits are found in Jo Daviess County in northwestern Illinois and in the fluorspar area of Hardin and Pope Counties in extreme southern Illinois. In northwestern Illinois the ore occurs in rocks of Ordovician age, but in southeastern Illinois it is associated with fluorspar in rocks of Mississippian age. ”

“ Pennsylvanian clays and shales are the most important source of clay for manufacturing such products as pottery, stoneware, drain tile, sewer pipe, flue tile, building tile, brick, and special heat-resistant fire-brick. ”

“ The key on the map shows the age sequence of the rocks, arranged with the youngest at the top, and gives the names that geologists have assigned to the various systems of rocks. Each system consists of rocks that were deposited during a long period of time. ”

“ Except for small areas along the Mississippi and Illinois River Valleys, these older rocks are found at the surface only in the northern quarter of the state and locally in Alexander, Hardin, Jackson, Monroe, Pike, and Union Counties. They are nevertheless economically important because they yield limestone, dolomite, silica sand, oil, zinc and lead, tripoli, novaculite, and novaculite gravel. ”

“ Such knowledge is shared with the public through publications, maps, lectures, and personal consultations with industries, drillers, engineers, land owners, teachers, and others in need of geologic information. ”