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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .DeC. 19,
the smaller valley of Woolhope. The latter has been described by
Sir R. Murchison, and more recently by Mr. Phillips*. It is 4^
miles in diameter, and resembles in size as well as in some of its
leading features the Caldera of Palma, the beds, in the boundary
cliifs encircling the excavated space, dipping in all directions outwards,
and the cliffs for that reason retaining more easily their steepness or
verticality.
3rdly. If the crater of a submarine volcano be upraised and begin
to emerge, the sea will still flow into it on its lowest side, and the
circular basin will then be filled and emptied alternately by the flux
and reflux of the tide, or by the rise of water blown into the opening
by prevailing winds, and then falling again as soon as this force ceases
to act, by which means a passage will be kept open, the crater being
scoured out like estuaries which have narrow entrances. On the
efiicacy of this last mode of aqueous erosion I must particularly insist,
as it aids us more than any other in comprehending the theory of denu-
dation-craters. The Basin of Mines in the Bay of Fundy illustrates
the manner in which a large bay, communicating with the ocean by
a narrow strait, may be filled and half-emptied every tide, so that
the waves and currents may sweep out in the course of centuries a
vast volume of mud and sand, and produce on all sides of the bay
long ranges of cliffs annually undermined, several hundred feet per-
pendicular, some composed of soft red marl, others of hard quartzose
grit, and others of columnar basalt. The Bay of Fundy it is true
would not present, if it were upraised and laid dry, so circular a hol-
low as the so-called crater of elevation, but there are numerous coves
on a part of the coast of Dorsetshire which are as perfectly circular,
if not more so than the Gulf of Santorin or the Caldera of Palma,
and in which the single breach effected by the sea on one side is not
larger in proportion to the entire girdle of encircling cliffs. These
cliffs moreover, which every geologist attributes exclusively to the
denuding action of the sea, are precipitous, and most lofty at the
head of the bay or farthest from the entrance, where they consist of
inclined strata of chalk. Lulworth Cove, which is 1300 feet across,
is the most perfect example (see fig. 3). In this case the hardness of
Fig. 3.
Coast of Dorsetshire.
Lulworth Cove

• Murchison, Silurian System, Part I. p. 428, and J. Phillips, Mem. of Geol.