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National Geologic Map Database
A collection of stratigraphic and related resources for scientists,
and for compiling and maintaining Geolex.
North American Stratigraphic Code

This Code describes how to classify and name all formally defined geologic units shown on maps and sections. It is the basis for the stratigraphic terminology used in the U.S. and compiled into Geolex.
See also:
NACSN website
Revision to Article 37 (Complex) of The Code (Easton and others, 2016)

Correlation Charts

Correlation charts and stratigraphic sections provide essential two- and three-dimensional context for the geologic names described in Geolex and in statewide and regional lexicons. Selected charts, sections, and lexicons are provided here.

USGS Index Cards

The Geologic Name Committee's (GNC) large collection of index cards citing references for geologic names (maintained ca. 1900-1990), here offered as a supplemental source of information on geologic names.

USGS Lexicons

Since the late 1800's, the U.S. Geological Survey has been responsible for maintaining a lexicon of geologic names for the Nation. Copies of previously published USGS lexicons are provided here, for quick reference.

Geologic time scales

A brief list of current and past geologic time scales

AAPG Geologic Provinces

For stratigraphic records in Geolex, we continue the established practice of assigning one or more "Geologic Provinces", to indicate where the geologic unit is known to occur. These provinces were defined by the Association of Petroleum Geologists; this province map is shown here.

List of Journals

Articles in scientific journals and society publications are checked peridocially for stratigraphic information that could be included in Geolex. This list of journals is provided as an additional resource for your stratigraphic studies.

State Geological Surveys

A list of the State Geological Surveys, where you may purchase or download publications related to stratigraphy.