The western moiety of this parish runs much further south than the
eastern, stretching in an irregular form into the granite near
Roughton and Brown Walley.
The rocks adjoining this granitic portion are compost and schistose
felspar, as at Alternun, and in a similar position. These are
succeeded in the vicinity of the church by a peculiar calcareous rock,
consisting almost entirely of hornblend and calcareous spar. The
northern part makes part of a downs, extending almost to Launceston,
and abounding in manganese.