13/16 These were principally: _Mare Serenitatis_, the Sea of Serenity, 25 deg. west, comprising a surface of about 130 thousand square miles; _Mare Crisium_, the Sea of Crises, a round, well defined, dark depression towards the northwestern edge, 17 deg. west, embracing a surface of 60 thousand square miles, a regular Caspian Sea in fact, only that the plateau in which it lies buried is surrounded by a girdle of much higher mountains. |