Geologic map of the Maurolycus Quadrangle of the Moon

Although geologic mapping fo the Moon has its own techniques and problems, systematic observation and the application of established geological principles have allowed the materials and structures of its surface to be delineated and classified into units (Shoemaker and Hackman 1962; McCauley 1967; Wilhelms, 1970). Most of these units are material entities similar to terrestrial rock-stratigraphic units and have been arranged in chronological sequence to form a lunar stratigraphic column. Relative ages are determined by superposition, embayment and cross cutting relations, and by density of superposed craters and degree of topographic freshness (Wilhelms 1970). In addition, crater morphologies are believed to be age dependent and departures from an original crater form can be used to establish relative age classes (Pohn and Offield, 1970). These classes have been dated relative to the units which define the lunar time-stratigraphic systems (Offield, 1971). The most important information, aside from the valuable data obtained from Apollo material samples, is gathered from Lunar Orbiter high-resolution photographs. These photographs have resolutions superior to the best earth-based telescopic observations, and geologic mapping and interpretation have reached a correspondingly high level of confidence.