The GeoRef database, established by the American Geosciences Institute (AGI) in 1966, provides access to the most comprehensive geoscience literature of the world. GeoRef contains millions of references to geoscience maps, serial, and non-serial literature. The database includes references to all publications of the U.S. Geological Survey. Master's theses and doctoral dissertations from US and Canadian universities are also covered. Coverage for North American resources starts in 1669, whereas worldwide coverage starts in 1933.