into the sea and disappears. On the south side the dip is gradual, on the
north side it is more abrupt, as is shown in Figure 2. As neither the
calcareous stratum, nor the superincumbent basaltic lava (as far as the
latter can be distinguished from the more modern ejections), appears to
thicken as it dips, I infer that these strata were not originally
accumulated in a trough, the centre of which afterwards became a point of
eruption; but that they have subsequently been disturbed and bent. We may
suppose either that Signal Post Hill subsided after its elevation with the
surrounding country, or that it never was uplifted to the same height with
it. This latter seems to me the most probable alternative, for during the
slow and equable elevation of this portion of the island, the subterranean
motive power, from expending part of its force in repeatedly erupting
volcanic matter from beneath this point, would, it is likely, have less
force to uplift it. Something of the same kind seems to have occurred near
Red Hill, for when tracing upwards the naked streams of lava from near
Porto Praya towards the interior of the island, I was strongly induced to
suspect, that since the lava had flowed, the slope of the land had been
slightly modified, either by a small subsidence near Red Hill, or by that
portion of the plain having been uplifted to a less height during the
elevation of the whole area.

THE BASALTIC LAVA, SUPERINCUMBENT ON THE CALCAREOUS DEPOSIT.

This lava is of a pale grey colour, fusing into a black enamel; its
fracture is rather earthy and concretionary; it contains olivine in small
grains. The central parts of the mass are compact, or at most crenulated
with a few minute cavities, and are often columnar. At Quail Island this
structure was assumed in a striking manner; the lava in one part being
divided into horizontal laminae, which became in another part split by
vertical fissures into five-sided plates; and these again, being piled on