e loftiest points upon their walls! There
is a chasm, 140 miles long and 70 broad, named Newton, situated about
200 miles from the south pole of the moon, whose floor lies 24,000 feet
below the summit of a peak that towers just above it on the east! This
abyss is so profound that the shadows of its enclosing precipices never
entirely quit it, and the larger part of its bottom is buried in endless
night.

One can not but shudder at the thought of standing on the broken walls
of Newton, and gazing down into a cavity of such stupendous depth that
if Chimborazo were thrown into it, the head of the mighty Andean peak
would be thousands of feet beneath the observer.

A different example of the crater mountains of the moon is the
celebrated Tycho, situated in latitude about 43 deg. south, corresponding
with the latitude of southern New Zealand on the earth. Tycho is nearly
circular and a little more than 54 miles across. The highest point on
its wall is about 17,000 feet above the interior. In the middle of its
floor is a mountain 5,000 or 6,000 feet high. Tycho is especially
remarkable for the vast system of whitish streaks, or rays, which
starting from its outer walls, spread in all directions over the face of
the moon, many of them, running, without deviation, hundreds of miles
across mountains, craters, and plains. These rays are among the greatest
of lunar mysteries, and we shall have more to say of them.

[Illustration: THE LUNAR ALPS, APENNINES, AND CAUCASUS.
Photographed with the Lick Telescope.]

Copernicus, a crater mountain situated about 10 deg. north of the equator,
in the eastern hemisphere of the moon, is another wonderful object, 56
miles in diameter, a polygon appearing, when not intently studied, as a
circle, 11,000 or 12,000 feet deep, and having a group of relatively low
peaks in the center of its floor. Around Copernicus an extensive area of
the moon's surface is whitened with something resembling the rays of
Tycho, but more irregular in appearance. Copernicus lies within the edge
of the great plain named the _Oceanus Procellarum_, or "Ocean of
Storms," and farther east, in the midst of the "ocean," is a smaller
crater mountain, named Kepler, which is also enveloped by a whitish
area, covering the lunar surface as if it were the result of extensive
outflows of light-colored lava.

In one important particular the crater mountains of the moon differ from
terrestrial volcanoes. This difference is clearly