e is given to the bright highlands
extending east of Gassendi towards Mersenius, forming the north-eastern
border of the Mare Humorum. They abound in minute detail--bright little
mountains and ridges--and include some clefts pertaining to the Mersenius
rill-system; but their most noteworthy feature is the long bright
mountain-arm, branching out from the eastern wall of Gassendi, and
extending for more than 50 miles towards the south-east.

The principal ranges on the limb are the _Leibnitz Mountains_, extending
from S. lat. 70 deg. on the west to S. lat. 80 deg. on the east limb.
They include some giant peaks and plateaus, noteworthy objects in
profile, some of which, according to Schroter and Madler, rise to 26,000
feet. The _Dorfel Mountains_, between S. lat. 80 deg. and 57 deg. on the
eastern limb, include, if Schroter's estimate is correct, three peaks
which exceed 26,000 feet. On the eastern limb, between S. lat. 35 deg.
and 18 deg., extend the _Rook Mountains_, which have peaks, according to
Schroter, as high as 25,000 feet. Next in order come the _Cordilleras_,
which extend to S. lat. 8 deg., and the _D'Alembert Mountains_, lying
east of Rocca and Grimaldi, closely associated with them, and probably
part of the same system. Some of the peaks approach 20,000 feet. In
addition to these mountain ranges there are others less prominent on the
limb in the northern hemisphere, which have not been named.

ISOLATED MOUNTAINS are very numerous in different parts of the moon, the
most remarkable are referred to in the appendix. Many remain unnamed.

CLEFTS OR RILLS.--Though Fontenelle, in his _Entretiens sur la Pluralite
des Mondes_, informs his pupil, the Marchioness, that "M. Cassini
discovered in the moon something which separates, then reunites, and
finally loses itself in a cavity, which from its appearance seemed to be
a river," it can hardly be supposed that what the French astronomer saw,
or fancied he saw, with the imperfect telescopes of that day, was one of
the remarkable and enigmatical furrows termed clefts or rills, first
detected by the Hanoverian selenographer Schroter; who, on October 7,
1787, discovered the very curious serpentine cleft near Herodotus, having
a few nights before noted for the first time the great Alpine valley west
of Plato, once classed with the clefts, though it is an object of a very
different kind. Between 1787 and 1797 Schroter found ten rills; but
twenty years elapsed before an addi