This parish is principally composed of strata of red and greenish-grey
slate, inclosing here and there beds of a compact quartzose rock.
These rocks are all similar to those of St. Anthony, and to those in
the cliff under Mount Edgcumbe, and at Saltash; but whether they
belong to the calcareous series, or to a more recent one associated
with the fossilliferous limestone of Plymouth, remains to be
ascertained.