This parish, like the last, rests only on granite; at low water,
however, some felspathic rocks may be seen.
The granite exhibits the common varieties of this part of Cornwall,
and is traversed by porphyritic beds; one of which at Mean is a
compound of granular felspar and shorl in various proportions. This
kind is of rare occurrence; it is traversed by veins of quartz, which
are occasionally much intermixed with shorl; this mineral also abounds
in the adjoining granite, but more particularly in the veins by which
it is traversed.
Whitsand Bay is covered with a testaceous sand like that of St. Ives,
of Padstow, and of other places on the north coast; a large tract of
this sand is exposed at low water to the action of the wind, by which
it has been drifted in considerable quantities inland so far as Sennen
Green.