Use the Library of Congress Subject Headings to determine the appropriate subject heading to look under. If a map is not listed under the smallest specific area you are interested in, look under the next larger area. C. Use Earth Sciences Disc . The disc is avaliable at the Science- Engineering Reference Desk. D. Use index maps.
Index maps show the areal coverage of the maps they index.
They may be limited in the types of maps they index, their publication dates, or other criteria. Make sure you understand what the index is indexing. For most of the states the U.S.G.S. has prepared geologic map indexes. It is in 6 sheets and includes indexing of maps in text series. Most of these monographs and series will be available in the Science-Engineering Library.