The rocks of this parish, like those of Gwinear adjoining, belong to
the prophyritic series; the northern part is covered with hillocks of
sand, a considerable portion of which, as on some part of Gwithian,
has been drifted from place to place by the action of the wind; this
to a certain extent is now prevented by a covering of arenaceous
plants, the extensive fibrous roots of which form a loose spongy net
work, which serves to retain the sand in its place. This sand was
originally of marine origin, being at low levels entirely composed of
fragments of marine shells; but inland, on more elevated places, a
considerable portion of terrestrial shell enters into its composition:
these have been derived from the myriads of the snail tribe, which
browse on the scanty herbage of these dreary _Towans_. The inland
drifts, after a strong wind, will be found to consist almost entirely
of the fragments of those land shells. On the coast this testaceous
sand is in several places consolidated into calcareous sandstone; but
this has taken place on a more extended scale in the parish of
Crantock.