nting to our gaze the
shattered and upturned fragments of the Moon's crust, convulsed by
forces of a volcanic nature which have long since expended their
energies and died out. The mountain ranges on the Moon resemble those of
the Earth, but they have a more rugged outline, and their peaks are more
precipitous, some of them rising to a height of 20,000 feet. They are
called the Lunar Alps, Apennines, and Cordilleras, and embrace every
variety of hill, cliff, mound, and ridge of comparatively low
elevation. The plains are large level areas, which are situated on
various parts of the lunar surface; they are of a darker hue than the
mountainous regions by which they are surrounded, and were at one time
believed to be seas. They are analogous to the prairies, steppes, and
deserts of the Earth.

_Valleys._--Some of these are of spacious dimensions; others are narrow,
and contract into gorges and chasms. Clefts or rills are long cracks or
fissures of considerable depth, which extend sometimes for hundreds of
miles across the various strata of which the Moon's crust is composed.

The characteristic features of the Moon's surface are the crater
mountains: they are very numerous on certain portions of the lunar disc,
and give the Moon the freckled appearance which it presents in the
telescope, and which Galileo likened to the eyes in the feathers of a
peacock's tail. They are believed to be of volcanic origin, and have
been classified as follows: 'Walled plains, mountain rings, ring plains,
crater plains, craters, craterlets, and crater cones.' Upwards of 13,000
of these mountains have been enumerated, and 1,000 are known to have a
diameter exceeding nine miles. Walled plains consist of circular areas
which have a width varying from 150 miles to a few hundred yards. They
are enclosed by rocky ramparts, whilst the centre is occupied by an
elevated peak. The depth of these formations, which are often far below
the level of the Moon's surface, ranges from 10,000 to 20,000 feet.
Mountain rings, ring plains, and crater plains resemble those already
described, but are on a smaller scale; the floors of the larger ones are
frequently occupied by craters and craterlets. The latter exist in large
numbers, and some portions of the Moon's surface appear honeycombed with
them, the smaller craters resting on the sides of larger ones and
occupying the bottoms of the more extensive areas. There is no kind of
formation on the Earth's surface th