pleasanter to make than on the dazzling highlands, and that the lunar
"sea" is to the working selenographer like an oasis in the desert to the
traveller--a relief in this case, however, not to an exhausted body, but
to a weary eye.

RING-MOUNTAINS, CRATERS, &C.--It is these objects, in their almost
endless variety and bewildering number, which, more than any others, give
to our satellite that marvellous appearance in the telescope which since
the days of Galileo has never failed to evoke the astonishment of the
beholder. However familiar we may be with the lunar surface, we can never
gaze on these extraordinary formations, whether massed together
apparently in inextricable confusion, or standing in isolated grandeur,
like Copernicus, on the grey surface of the plains, without experiencing,
in a scarcely diminished degree, the same sensation of wonder and
admiration with which they were beheld for the first time. Although the
attempt to bring all these _bizarre_ forms under a rigid scheme of
classification has not been wholly successful, their structural
peculiarities, the hypsometrical relation between their interior and the
surrounding district, their size, and the character of their
circumvallation, the dimensions of their cavernous opening as compared
with that of the more or less truncated conical mass of matter
surrounding it, all afford a basis for grouping them under distinctive
titles, that are not only convenient to the selenographer, but which
undoubtedly represent, as a rule, actual diversities in their origin and
physical character.

These distinguishing titles, as adopted by Schroter, Lohrmann, and
Madler, and accepted by subsequent observers, are WALLED-PLAINS, MOUNTAIN
RINGS, RING-PLAINS, CRATERS, CRATER-CONES, CRATERLETS, CRATER-PITS,
DEPRESSIONS.