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cannot be denied that some of them may very possibly be thebeds of defunct oceans, by which, in ages long past, they mayhave been covered.
In addition to the large ring-mountains of which we wererecently speaking, there are many circular formations, ofwhich some beautiful examples are to be seen in the platewhich contains the view of Copernicus , so small as to bemore justly called craters ; while to others, smaller still, thename of craterlets, or crater-pits, has been given. In cer-tain regions these minute craterlets, varying from less thana mile to live or six miles in diameter, are exceedinglynumerous.
It is very interesting, even with a small telescope, to com-pare the Moon with a good outline lunar map ; * to identifythe various mountains by name; to note those which aredistinguished by central cones, or by other peculiarities; toobserve the long pointed shadows of the summit's of the Apen-nines ; or to search for occasional instances of isolated peaksof a more or less conical shape. One of the most remarkableof these is named Pico. It is about 7,000, or, perhaps, 8,000feet high, and may be found near to the lunar Alps.
There are other peculiarities of the lunar surface, moredifficult to detect than those which we have hitherto men-tioned; the most important being termed clefts, or rills.t Someof these present an appearance very similar to that whichwould be afforded by the bed of an extinct torrent or river,and may possibly resemble the canons of North-WestAmerica. Others are so straight and regular that they mightalmost make us imagine that they must have been artificialh rconstructed, were it not that many reasons discountenancesuch a supposition. They are traceable for great distances, and
* Such maps may be found in Webb’s “ Celestial Objects, ” and, upon alarger scale, in “ The Moon, ” by Mr. J7eison ; the most elaborate of allbeing that of Dr. Julius Schmidt, 6 Paris feet in diameter, published in1878, at the expense of the Prussian Government.
t This word, adopted from the German “ rillen ,” is not intended inan y wise to imply the existence of water, as would be the case with themore usual meaning of the English word.