farther. In some ravines at right angles to the coast, it is seen gently
dipping towards the sea, probably with the same inclination as when
deposited round the ancient shores of the island. I found only one inland
section, namely, at the base of the hill marked A, where, at the height of
some hundred feet, this bed was exposed; it here rested on the usual
compact augitic rock associated with wacke, and was covered by the
widespread sheet of modern basaltic lava. Some exceptions occur to the
horizontality of the white stratum: at Quail Island, its upper surface is
only forty feet above the level of the sea; here also the capping of lava
is only between twelve and fifteen feet in thickness; on the other hand, at
the north-east side of Porto Praya harbour, the calcareous stratum, as well
as the rock on which it rests, attain a height above the average level: the
inequality of level in these two cases is not, as I believe, owing to
unequal elevation, but to original irregularities at the bottom of the sea.
Of this fact, at Quail Island, there was clear evidence in the calcareous
deposit being in one part of much greater than the average thickness, and
in another part being entirely absent; in this latter case, the modern
basaltic lavas rested directly on those of more ancient origin.

Under Signal Post Hill, the white stratum dips into the sea in a remarkable
manner. This hill is conical, 450 feet in height, and retains some traces
of having had a crateriform structure; it is composed chiefly of matter
erupted posteriorly to the elevation of the great basaltic plain, but
partly of lava of apparently submarine origin and of considerable
antiquity. The surrounding plain, as well as the eastern flank of this
hill, has been worn into steep precipices, overhanging the sea. In these
precipices, the white calcareous stratum may be seen, at the height of
about seventy feet above the beach, running for some miles both northward
and southward of the hill, in a line appearing to be perfectly horizontal;
but for a space of a quarter of a mile directly under the hill, it dips