(LAC-38) Geologic map of the Seleucus quadrangle of the moon

The surface of the Moon is heterogenous. Local surfaces can be classed on the basis of telescopic observations into units, each having a limited range of physical properties such as topography, visible under low illumination. The properties of such surface units are considered to represent properties of under lying materials, so that the surface units correspond to underlying rock units which are analogous to the rock-stratigraphic formations of terrestrial geology. These rock units are arranged in order of relative age and grouped into time stratigraphic units by application of the concepts of superposition and intersection, and by their apparent modification of properties with time. Following terrestrial convection, the major time-stratigraphic units are designated systems; the three systems recognized to date are Imbrian, Eratosthenian and Copernican. The type localities of the systems are in the vicinity of Mare Imbrium (Shoemaker, 1962; Shoemaker and Hackman 1962).