mouthed crater, standing nearly in the position of Green Mountain, like a
great air-gun, shot forth, before its final extinction, this vast
accumulation of loose matter. Subsequently to this event, considerable
dislocations have taken place, and an oval circus has been formed by
subsidence. This sunken space lies at the north-eastern foot of Green
Mountain, and is well represented in Map 2. Its longer axis, which is
connected with a N.E. and S.W. line of fissure, is three-fifths of a
nautical mile in length; its sides are nearly perpendicular, except in one
spot, and about four hundred feet in height; they consist, in the lower
part, of a pale basalt with feldspar, and in the upper part, of the tuff
and loose ejected fragments; the bottom is smooth and level, and under
almost any other climate a deep lake would have been formed here. From the
thickness of the bed of loose fragments, with which the surrounding country
is covered, the amount of aeriform matter necessary for their projection
must have been enormous; hence we may suppose it probable that after the
explosions vast subterranean caverns were left, and that the falling in of
the roof of one of these produced the hollow here described. At the
Galapagos Archipelago, pits of a similar character, but of a much smaller
size, frequently occur at the bases of small cones of eruption.

EJECTED GRANITIC FRAGMENTS.

In the neighbourhood of Green Mountain, fragments of extraneous rock are
not unfrequently found embedded in the midst of masses of scoriae.
Lieutenant Evans, to whose kindness I am indebted for much information,
gave me several specimens, and I found others myself. They nearly all have
a granitic structure, are brittle, harsh to the touch, and apparently of
altered colours.

FIRST, a white syenite, streaked and mottled with red; it consists of well-