ot only
more rugged and uneven, but is covered to a much greater extent with
numbers of quasi-circular formations, differing widely in size, classed
as walled-plains, ring-plains, craters, craterlets, crater-cones, &c.
(the latter bearing a great outward resemblance to some terrestrial
volcanoes), and mountain ranges of vast proportions, isolated hills, and
other features.

Though nothing resembling sheets of water, either of small or large
extent, have ever been detected on the surface, the superficial
resemblance, in small telescopes, of the large grey tracts to the
appearance which we may suppose our terrestrial lakes and oceans would
present to an observer on the moon, naturally induced the early
selenographers to term them Maria, or "seas"--a convenient name, which
is still maintained, without, however, implying that these areas, as we
now see them, are, or ever were, covered with water. Some, however,
regard them as old sea-beds, from which every trace of fluid, owing to
some unknown cause, has vanished, and that the folds and wrinkles, the
ridges, swellings, and other peculiarities of structure observed upon
them, represent some of the results of alluvial action. It is, of course,
possible, and even probable, that at a remote epoch in the evolution of
our satellite these lower regions were occupied by water, but that their
surface, as it now appears, is actually this old sea-bottom, seems to be
less likely than that it represents the consolidated crust of some semi-
fluid or viscous material (possibly of a basaltic type) which has welled
forth from orifices or rents communicating with the interior, and
overspread and partially filled up these immense hollows, more or less
overwhelming and destroying many formations which stood upon them before
this catastrophe took place. Though this, like many other speculations of
a similar character relating to lunar "geology," must remain, at least
for the present, as a mere hypothesis; indications of this partial
destruction by some agency or other is almost everywhere apparent in
those formations which border the so-called seas, as, for example,
Fracastorius in the Mare Nectaris; Le Monnier in the Mare Serenitatis;
Pitatus and Hesiodus, on the south side of the Mare Nubium; Doppelmayer
in the Mare Humorum, and in many other situations; while no observer can
fail to notice innumerable instances of more or less complete
obliteration and ruin among objects within these areas,