The rocks of the southern part of this parish resemble those of St.
Ervan, but near the church a lamelar blue slate prevails, like that of
Endellion, and like it also abounding in veins of the sulphurets of
lead and of antimony.
The western part of the parish, which extends into the sea, forming a
promontory called Trevose Head, is composed of crystalline rocks,
which are massive, and differ from all the rocks that are interposed
between it and the granite of St. Dennis. Both the composition and the
relative situation of these rocks are very interesting. They appear to
be the equivalents of the masses of serpentine of Clicker Tor, and of
the Lizard district; of the felspathic rocks which form the downs
between Launceston and Davidstow; and of that curious mass of rock at
King Arthur’s Castle, in Tintagel. Geologists have yet to learn the
precise relation of these crystalline masses with the calcareous
series in which they are situated.