to some of the ridges on the moon is unquestionable; and if we could
believe that the Maria, as we now see them, are dried-up sea-beds, it
might be concluded that these ridges had a similar origin; but their
close connection with centres of volcanic disturbance, and the numbers of
little craters on or near their track, point to the supposition that they
consist rather of material exuded from long-extending fissures in the
crust of the "seas," and in other surfaces where they are superimposed.
This conjecture is rendered still more probable by the fact that we
sometimes find the direction of clefts (which are undoubted surface
cracks) prolonged in the form of long narrow ridges or of rows of little
hillocks. We are, however, not bound to assume that all the manifold
corrugations observed on the lunar plains are due to one and the same
cause; indeed, it is clear that some are merely the outward indications
of sudden drops in the surface, as in the case of the ridges round the
western margin of the Mare Nectaris, and in other situations, where
subsidence is manifested by features assuming the outward aspect of
ordinary ridges, but which are in reality of a very different structural
character.

The Maria, like almost every other part of the visible surface, abound in
craters of a minute type, which are scattered here and there without any
apparent law or ascertained principle of arrangement. Seeing how
imperfect is our acquaintance with even the larger objects of this class,
it is rash to insist on the antiquity or permanence of such diminutive
objects, or to dogmatise about the cessation of lunar activity in
connection with features where the volcanic history of our globe, if it
is of any value as an analogue, teaches us it is most likely to prevail.

Most observers will agree with Schmidt, that observations and drawings of
objects on the sombre depressed plains of the moon are easier and