Smithsonian Report, 1928. — Barrell 



Plate 3 



The Mare Imbrium and Its Surroundings, Northeast Quadrant of the 



Moon 



The floor of the mare is seen to be older than the ray system of Copernicus and the small, sharp-lipped 

 craters scattered over it. The mare is younger, however, than the rough topography within its walls 

 on the left. On the northern (lower) border of Imbrium is seen the crater Plato, 60 miles in diameter 

 and with crater walls 4,000 feet high. It is flooded by lava which appears to be related to that of 

 the mare. On the right, near the sunrise line, is preserved the half of a still larger circle, opening 

 into the mare and forming the Sinus Iridum. (Photograph by Yerkes Observatory) 



