The Survey has issued numerous reports that deal with the resources discussed here and mimeographed lists of these are available upon request. If reproduction is made of the material herein, acknowledgment of the Illinois State Geological Survey is requested. 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_.