h rose up in the principal crater, and that the second shoal
marks the site of the submarine eruption observed in August, 1831, to
the S. W. of the island.

From the whole of the facts above detailed, it appears that a hill eight
hundred feet or more in height was formed by a submarine volcanic vent,
of which the upper part (only about two hundred feet high) emerged above
the waters, so as to form an island. This cone must have been equal in
size to one of the largest of the lateral volcanoes on the flanks of
Etna, and about half the height of the mountain Jorullo in Mexico, which
was formed in the course of nine months, in 1759. In the centre of the
new volcano a large cavity was kept open by gaseous discharges, which
threw out scoriae; and fluid lava probably rose up in this cavity. It is
not uncommon for small subsidiary craters to open near the summit of a
cone, and one of these may have been formed in the case of Graham
Island; a vent, perhaps, connected with the main channel of discharge
which gave passage in that direction to elastic fluids, scoriae, and
melted lava. It does not appear that, either from this duct, or from the
principal vent, there was any overflowing of lava; but melted rock may
have flowed from the flanks or base of the cone (a common occurrence on
land), and may have spread in a broad sheet over the bottom of the sea.

[Illustration: Fig. 62.

Supposed section of Graham Island. (C. Maclaren.[599])]

The dotted lines in the annexed figure are an imaginary restoration of
the upper part of the cone, now removed by the waves: the strong lines
represent the part of the volcano which is still under water: in the
centre is a great column, or dike, of solid lava, two hundred feet in
diameter, supposed to fill the space by which the gaseous fluids rose;
and on each side of the dike is a stratified mass of scoriae and
fragmentary lava. The solid nucleus of the reef, where the black rock is
now found, withstands the movements of the sea; while the surrounding
loose tuffs are cut away to a somewhat lower level. In this manner the
lava, which was the lowest part of the island, or, to speak more
correctly, which scarcely ever rose above the level of the sea when the
island existed, has now become the highest point in the reef.

No appearances observed, either during the eruption or since the island
disappeared, gave the least support to the opinion promulgated by some
writers, that part of the ancient be