This book was prepared by the Educational Extension Section of the Illinois State Geological Survey, principally Betty Jean Hanagan, I. Edgar Odom, and Shirley J. Trueblood, under the direction of George M. Wilson. They were assisted by other members of the Survey staff, especially J. E. Lamar and J. C. Bradbury of the Industrial Minerals Section. Educational Extension also serves the public by assembling and distributing rock and mineral collections for Illinois educational groups, giving lectures, preparing exhibits, answering queries about identification of rocks and minerals, reporting Survey news, and conducting earth science field trips. During each year six field trips are conducted in widely separated parts of the state for teachers, students, and laymen. The general program is especially designed to assist in teaching the earth sciences and to help make Illinois citizens aware of the state’s great mineral wealth. Illinois State Geological Survey Urbana, Illinois [Illustration: ILLINOIS _Land of Lincoln_] Transcriber’s Notes —Silently corrected a few typos. —Retained publication information from the printed edition: this eBook is public-domain in the country of publication. —In the text versions only, text in italics is delimited by _underscores_.