other words,
where the outburst of the Kaimenis has been witnessed in historical
times. The single long and deep opening into the crater is a feature
common to all those remnants of ancient volcanoes, the central portions
of which have been removed, and is probably connected with aqueous
denudation. This denuding process has been the work of ages when the sea
was admitted into an original crater, and has taken place during the
gradual emergence of the island from the sea, or during various
oscillations in its level.

The volcanic island of St. Paul in the midst of the Indian Ocean, lat.
38 degrees 44 minutes S., long. 77 degrees 37 minutes E., surveyed by
Capt. Blackwood in 1842, seems to exemplify the first stage in the
formation of such an archipelago as that of Santorin. We have there a
crater one mile in diameter, surrounded by steep and lofty cliffs on
every side save one, where the sea enters by a single passage nearly dry
at low water. In the interior of the small circular bay or crater there
is a depth of 30 fathoms, or 180 feet. The surface of the island slopes
away on all sides from the crest of the rocks encircling the
crater.[614]

[Illustration: Fig. 66.

Cone and crater of Barren Island, in the Bay of Bengal. Height of the
central cone (according to Capt Miller, in 1834), 500 feet.]

_Barren Island._--There is great analogy between the structure of Barren
Island in the Bay of Bengal, lat. 12 degrees 15 minutes, and that of
Santorin last described. When seen from the ocean, this island presents,
on almost all sides, a surface of bare rocks, rising, with a moderate
acclivity, towards the interior; but at one point there is a cleft by
which we can penetrate into the centre, and there discover that it is
occupied by a great circular basin, filled by the waters of the sea, and
bordered all around by steep rocks, in the midst of which rises a
volcanic cone, very frequently in eruption. The summit of this cone is
about 500 feet in height, corresponding to that of the circular border
which incloses the basin; so that it can be seen from the sea only
through the ravine. It is most probable that the exterior inclosure of
Barren Island (_c_, _d_, fig. 67) is nothing more than the remains of a
truncated cone _c_, _a_, _b_, _d_, a great portion of which has been
removed by engulfment, explosion, or denudation, which may have preceded
the formation of the new interior cone, _f_, _e_, _g_.[615]

[Illustration: Fig