This mosaic of Apollo 17 frames extends across southern Mare Serenitatis, one of the larger multiringed basins on the Moon's near side (fig. 14). The average diameter of the basin is about 680 km. Its generally circular outline is mimicked by the systems of arcuate rilles near the outer edge of the basin and also by the large system of mare ridges extending from arrow to arrow. Another feature of Mare Serenitatis is the nearly continuous ring of dark mare material that occupies the outer part of its floor. When these pictures were taken, the Sun angle was too low to show differences in albedo clearly. However, part of the ring of dark mare material is visible near the Plinius Rilles (Rimae Plinius) and the Littrow Rilles (Rimae Littrow). The stratigraphic relationships between the dark and light mare units are described in figure 59, which is an enlargement of the small area outlined in this figure.  -G.W.C.