the plain, to which their flanks descend with a steep declivity. The
counterscarp of the Apennines, in places 160 miles in width from east to
west, runs down to the Mare Vaporum with a comparatively gentle
inclination. It is everywhere traversed by winding valleys of a very
intricate type, all trending towards the south-west, and includes some
bright craters and mountain-rings. The _Carpathians_, forming in part the
southern border of the Mare Imbrium, extend for a length of more than 180
miles eastward of E., long. 16 deg., and, embracing the ring-plain Gay-
Lussac, terminate west of Mayer. They present a less definite front to
the Mare than the Apennines, and are broken up and divided by irregular
valleys and gaps; their loftiest peak, situated on a very projecting
promontory north-west of Mayer, rising to a height of 7000 feet.
Notwithstanding their comparatively low altitude, the region they occupy
forms a fine telescopic picture at lunar sunrise. The _Sinus Iridum
highlands_, bordering the beautiful bay on the north-east side of the
Mare Imbrium, rank among the loftiest and most intricate systems on the
moon, and, like the Apennines, present a steep face to the grey plain
from which they rise, though differing from them in other respects. They
include many high peaks, the loftiest, in the neighbourhood of the ring-
plain Sharp, rising 15,000 feet. There are probably some still higher
mountains in the vicinity, but the difficulties attending their
measurement render it impossible to determine their altitude with any
approach to accuracy.

_The Taurus Mountains_ extend from the west side of the Mare Serenitatis,
near Le Monnier and Littrow, in a north-westerly direction towards
Geminus and Berselius, bordering the west side of the Lacus Somniorum.
They are a far less remarkable system than any of the preceding, and
consist rather of a wild irregular mountain region than a range. In the
neighbourhood of Berselius are some peaks which, according to Neison,