dth,
is, owing to the shallowness of the component hills and valleys, a very
difficult object to see in its entirety, as it must be viewed when close
to the terminator, and even then the sun's azimuth and good definition do
not always combine to afford a satisfactory glimpse of its ramifications.
M. Gaudibert has given a drawing of it in the _English Mechanic_, vol.
xviii. p. 638.

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,-