ring-mountains, passing through gaps in
their walls as, for example, in the cases of Madler, Lassell, &c. Various
hypotheses have been advanced to account for them. The late Professor
Phillips, the geologist, who devoted much attention to the telescopic
examination of the physical features of the moon, compared the lunar
ridges to long, low, undulating mounds, of somewhat doubtful origin,
called "kames" in Scotland, and "eskers" in Ireland, where on the low
central plain they are commonly found in the form of extended banks
(mainly of gravel), with more or less steep sides, rising to heights of
from 20 to 70 feet. They are sometimes only a few yards wide at the top,
while in other places they spread out into large humps, having circular
or oval cavities on their summits, 50 or 60 yards across, and as much as
40 feet deep. Like the lunar ridges, they throw out branches and exhibit
many breaches of continuity. By some geologists they are supposed to
represent old submarine banks formed by tidal currents, like harbour
bars, and by others to be glacial deposits; in either case, to be either
directly or indirectly due to alluvial action. Their outward resemblance
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
cr