But everywhere the true craters are in evidence, even on the
sea-beds, although they attain their greatest number and size on those
parts of the moon -- covering sixty per cent of its visible surface --
which are distinctly mountainous in character and which constitute its
most brilliant portions. Broadly speaking, the southwestern half of
the moon is the most mountainous and broken, and the northeastern half
the least so. Right down through the center, from pole to pole, runs a
wonderful line of craters and crateriform valleys of a magnitude
stupendous even for the moon. Another similar line follows the western
edge. Three or four ``seas'' are thrust between these mountainous
belts. By the effects of ``libration'' parts of the opposite
hemisphere of the moon which is turned away from the earth are from
time to time brought into view, and their aspect indicates that that
hemisphere resembles in its surface features the one which faces the
earth. There are many things about the craters which seem to give some
warrant for the hypothesis which has been particularly urged by Mr G.
K. Gilbert, that they were formed by the impact of meteors; but there
are also many things which militate against that idea, and, upon the
whole, the volcanic theory of their origin is to be preferred.
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