have been greater when the Monte del Cavallo formed a more complete
circuit about the crater cone). But compare the dimensions. The
remains of the outer crater ring of Vesuvius are perhaps half a mile
in diameter, while the active crater itself is only two or three
hundred feet across at the most; Tycho has a diameter of fifty-four
miles! The group of relatively insignificant peaks in the center of
the crater floor of Tycho is far more massive than the entire mountain
that we call Vesuvius. The largest known volcanic crater on the earth,
Aso San, in Japan, has a diameter of seven miles; it would take sixty
craters like Aso San to equal Tycho in area! And Tycho, though one of
the most perfect, is by no means the largest crater on the moon.
Another, called ``Theophilus,'' has a diameter of sixty-four miles,
and is eighteen thousand feet deep. There are hundreds from ten to
forty miles in diameter, and thousands from one to ten miles. They are
so numerous in many places that they break into one another, like the
cells of a crushed honeycomb.

The lunar craters differ from those of the earth more fundamentally
than in the matter of mere size; they are not situated on the tops of
mountains. If they were, and if all the proportions were the same, a
crater like Tycho might crown a conical peak fifty or one hundred
miles high! Instead of being cavities in the summits of mountains, the
lunar craters are rather gigantic sink-holes whose bottoms in many
cases lie two or three miles below the general surface of the lunar
world. Around their rims the rocks are piled up to a height of from a
few hundred to two or three thousand feet, with a comparatively gentle
inclination, but on the inner side they fall away in gigantic broken
precipices which make the dizzy cliffs of the Matterhorn seem but
``lover's leaps.'' Down they drop, ridge below ridge, crag under crag,
tottering wall beneath wall, until, in a crater named ``Newton,'' near