This parish offers many objects of considerable interest to the
geologist. It is entirely situated on rocks belonging to the
calcareous series. In the southern part, its rocks consist of clay
slates possessing various degrees of fissibility, from the most
perfect roofing-slate of Delabole, to a slate that can only be
separated into thick flags. Amongst these strata occurs an interesting
rock, which appears to be composed of hornblende and compact felspar,
and in some parts of hornblende and calcareous spar only. The latter
variety is well known in the neighbourhood under the name of green
freestone, and may be seen in the walls of the oldest churches. It is
_in situ_ in a croft near the pretty little waterfall of Nathan’s or
Kneighton’s Kieve.
In the northern part of the parish, near King Arthur’s Castle, and in
Bossiney Cove, the slate is very _talcose_, and is occasionally coated
at its joints with calcareous spar. At the former place also occurs a
large mass of compact felspar, but which is so much decomposed that
its precise nature has not been ascertained. In the sea-cliffs are
several slate-quarries, the quality of which, however, is inferior to
the Delabole, and is known in the market by the name of _cliff slate_.
In this slate are impressions apparently derived from shells, which
have been referred to the genus _producta_. This is the only instance
of a fossiliferous slate hitherto detected in Cornwall, though it is
probable that others may exist, particularly between St. German’s and
the Rame Head.