In the late 1800’s, the U.S. Geological Survey, under the leadership of Director John Wesley Powell, began a systematic mapping program that produced the Geologic Atlas of the United States folios. Recognizing the need for a consistent set of geologic maps, he formed committees to develop standards for cartography, principles of rock and sediment classification and nomenclature, and a geological time scale. Essential to these standards and to the Atlas series was a catalog of geologic names of the U.S.
The catalog of geologic names remains essential to this day, both to the science and to preparation of the U.S. National Geologic Map Database (NGMDB, http://ngmdb.usgs.gov), a collaborative project managed by the USGS and the Association of American State Geologists as mandated by Congress. The U.S. Geologic Names Lexicon (GEOLEX) contains ~16,000 geologic units, and provides type and reference localities, geologic ages, geographic extent, variations in geologic name usage, and original and redefinitions; these are compiled mostly from formal reports and maps published since 1836, emphasizing outcrop-level descriptions, age determinations, and relationships to other geologic units. These reports are quite varied in nature, and the publishers range from local societies to state and national agencies.
Observations and interpretations made by geologists are even more varied in nature. Although the original definitions of many names are still in use today, many have been redefined numerous times, and some remain as "bones of contention" (e.g., variation in nomenclature of identical rock units on different sides of state boundaries), necessitating mention of the divergent views of the geologists. For a century, the U.S. Geologic Names Committee (GNC) has assisted geologists in their efforts to reconcile and clarify the nation’s stratigraphy. We are now scanning the collection of unpublished GNC notes; these will be used to supplement GEOLEX’s content, and hopefully will aid geologists in their current studies.
The scientific reports, maps, and GNC notes in GEOLEX are valuable, but by integrating this information with geologic map databases, their utility can be further enhanced. For example, we are combining GEOLEX content with spatial data in the NGMDB (i.e., the footprint of a map, or the digital map data) to provide our users with stratigraphic descriptions in their geographic context. Although geologic map databases allow for comprehensive documentation of geologic units (and even of individual geologic features such as observation points and outcrop areas), it is widely recognized that preparing this documentation can be a great burden to the geologist. We are developing mechanisms to encourage and facilitate a more informative and useful documentation of geologic units in these map databases; for example, to note the method of geologic age determination, revisions to unit boundaries, or areas where a unit was previously misidentified.