Doctor Boase remarks the eastern half of this parish is situate on
granite, which is of the same kind, and belongs to the same insulated
group, as that extending into the parishes of Advent and of Alternun.
The western half consists of alternate layers of schistone and of
compact rocks, some of which approach near to greenstone. These rocks
are, however, more fully exposed in the adjacent parish of St.
Breward, or Simonward, under which head they will be described.