Additional evidence of Mercurian volcanism

Evidence concerned with (1) the character and distribution of terrain surrounding fresh basins; (2) albedo, color, and temporal differences between a basin rim and smooth plains on its floor; and (3) the stratigraphic relations and local distribution of smooth plains in the hilly and lineated terrain are cited as additional evidence for an internal origin of much of the Mercurian smooth plains. Although the question of Mercurian volcanism should be kept open, this evidence together with that presented in an earlier paper suggests that volcanism occurred on Mercury early in its history.