Mare Marginis
Mare Marginis lies on the very edge of the lunar nearside. Thus, it lies
halfway between the lunar nearside and farside. It also differs from most
of the nearside maria. It has an irregular outline, and it appears to be
fairly thin. Note the small circular and elongated features in the mare
plains. These probably mark impact craters buried by less than
1000 - 1700 feet (300-500 meters) of lava. Further, Mare Marginis is not
centered on any clear, large
impact basin. Thus, Mare Marginis seems to mark a low-lying region of the
highlands where mare lavas were just able to reach the surface. Several
large mare-floored craters also occur nearby. In these craters, the crater
floors lie below the surrounding highland surface. Thus, they mark sites
around Mare Marginis where lavas were close to the lunar surface. (Lunar
Orbiter image IV-165-H3)