2.75; pure Carrara marble was found by Sir H. De la Beche to be 2.7.
("Researches in Theoretical Geology" page 12.) It is remarkable that these
rocks of Ascension, formed close to the surface, should be nearly as
compact as marble, which has undergone the action of heat and pressure in
the plutonic regions.

The great accumulation of loose calcareous particles, lying on the beach
near the Settlement, commences in the month of October, moving towards the
S.W., which, as I was informed by Lieutenant Evans, is caused by a change
in the prevailing direction of the currents. At this period the tidal
rocks, at the S.W. end of the beach, where the calcareous sand is
accumulating, and round which the currents sweep, become gradually coated
with a calcareous incrustation, half an inch in thickness. It is quite
white, compact, with some parts slightly spathose, and is firmly attached
to the rock. After a short time it gradually disappears, being either
redissolved, when the water is less charged with lime, or more probably is
mechanically abraded. Lieutenant Evans has observed these facts, during the
six years he has resided at Ascension. The incrustation varies in thickness
in different years: in 1831 it was unusually thick. When I was there in
July, there was no remnant of the incrustation; but on a point of basalt,
from which the quarrymen had lately removed a mass of the calcareous
freestone, the incrustation was perfectly preserved. Considering the
position of the tidal-rocks, and the period at which they become coated,
there can be no doubt that the movement and disturbance of the vast
accumulation of calcareous particles, many of them being partially
agglutinated together, cause the waves of the sea to be so highly charged
with carbonate of lime, that they deposit it on the first objects against
which they impinge. I have been informed by Lieutenant Holland, R.N., that
this incrustation is formed on many parts of the coast, on most of which, I
believe, there are likewise great masses of comminuted shells.