GEOLEX—THE U.S. GEOLOGIC NAMES LEXICON

In the late 1800’s, the USGS, under the leadership of Director John Wesley Powell, began mapping activities for the Geologic Atlas of the United States folios. Realizing the diversity of geologic areas being studied (e.g., Appalachians, Rocky Mountains) and of the geologists studying them, he determined that “a body of rules” covering the scope of publication, principles of rock and sediment classification and nomenclature, and geological time scale was essential in order to maintain a sense of uniformity among these folios. Geologists were convened to discuss these matters, and the U.S. Geologic Names Committee (GNC) was established.

During these past 100+ years, as ideas and practices in the geological sciences have evolved, the geoscience community has found it necessary at times to refine the standards of classification and nomenclature, and the time scale, to support the science. Today, the GNC follows the North American Commission on Stratigraphic Nomenclature’s guidelines for classifying and naming geologic units, and a modified version of the IUGS International geological time scale.

The GNC has since its inception maintained a catalog of geologic units of the U.S., and since 1902 has published formal geologic names lexicons. Record keeping has evolved from handwritten index cards to the present-day lexicon (GEOLEX), a component of the National Geologic Map Database Project (http://ngmdb.usgs.gov). It currently contains ~16,000 geologic units. In the northeastern U.S., there are ~2400 geologic units recognized by state geological surveys and the USGS. GEOLEX provides original and current definitions, type localities, geologic ages, geographic extent, variations in geologic name usage, and publication synopses. Information has been compiled mostly from formal reports and maps published since 1836, emphasizing outcrop-level descriptions, age determination techniques, and relationships to other geologic units.

Most geologic names documented in the GNC catalog and previous lexicons are available online. GEOLEX is a work in progress and is being supplemented with information from these archives, and from recent studies by the state geological surveys, USGS, and universities. Information not yet available through GEOLEX can be obtained from this author.