GAMBART.—­A regular ring-plain, 16 miles in diameter, with a low border and without visible detail within; situated nearly on the lunar equator, about 130 miles S.S.W. of Copernicus, at the N.W. edge of a very hilly region.  A prominent pear-shaped mountain, with a small crater upon it, stands a short distance on the S.W., and further in the same direction, a large bright crater with two much smaller craters on the N. of it.  The rough hilly district about midway between Copernicus and Gambart is remarkable for its peculiar dusky tone and for certain small dark spots, first seen by Schmidt, and subsequently carefully observed by Dr. Klein.  The noteworthy region where these peculiar features are found represents an area of many thousand square miles, and must resemble a veritable Malpais, covered probably with an incalculable number of craters, vents, cones, and pits, filled with volcanic debris.  It is among details of this character that the true analogues of some terrestrial volcanoes must be looked for.  Under a low angle of illumination the surface presents an extraordinarily rough aspect, well worthy of examination, but the dusky areas and the black spots can only be satisfactorily distinguished under a somewhat high sun.  I have, however, seen them fairly well when the W. wall of Reinhold was on the morning terminator.

MARCO POLO.—­A small and very irregularly-shaped enclosure (difficult to see satisfactorily) on the S. flank of the Apennines.  It is hemmed in on every side by mountains.

ERATOSTHENES.—­A noble ring-plain, 38 miles in diameter; a worthy termination of the Apennines.  The best view of it is obtained under morning illumination when the interior is about half-filled with shadow.  At this phase the many irregular terraces on the inner slope of the E. wall (which rises at one peak 16,000 feet above an interior depressed 8000 feet below the Mare Imbrium) are seen to the best advantage.  The central mountain is made up of two principal peaks, nearly central, from which two bright curved hills extend nearly up to the N.W. wall,—­the whole forming a V-shaped arrangement.  On the S. there is a narrow break in the wall, and the S.W. section of it seems to overlap and extend some distance beyond the S.E. section.  The border on the S.W. is remarkable for the great width of its glacis.  Eratosthenes exhibits a marked departure from circularity, especially on the E., where the wall consists of two well-marked linear sections, with an intermediate portion where the crest for 20 miles or more bends inwards or towards the centre.  From the S.E. flank of this formation extends towards the W. side of Stadius one of the grandest mountain arms on the moon’s visible surface, rising at one place 9000 feet, and in two others 5000 and 3000 feet respectively above the Mare Imbrium.  If this magnificent object is observed when the morning terminator falls a little E. of Stadius, it affords a spectacle not easily forgotten.  I have often seen it at this phase when its broad mass of shadow extended across the well-known crater-row W. of Copernicus, some of the component craters appearing between the spires of shade representing the loftiest peaks on the mountain arm.  There is a prominent little crater on the crest of the arm between two of the peaks, and another on the plain to the west.