A large portion of this parish is situated on granite, the boundary
line of which extends from near the church, in a semicircular form, to
Buryas Bridge. South of this line the parish consists of felspar,
hornblend, and actynolite rocks, all of which occur both in massive
and in schistose forms. A fine instance of the latter may be seen at
the back of the quay at Penzance, and may be traced for some distance
in a westerly direction on the sea shore below high-water mark. About
half way to Newlyn another bed of porphyry, or an irregular
continuation of the former, was a few years since explored for tin,
and became the celebrated Wherry Mine, yielding not only a large
quantity of tin, so as to afford profit after paying the expenses of a
steam-engine, but also beautiful specimens of rare metallic minerals.
For an account of this curious submarine mine, Mr. Hawkins’ Paper in
the Transactions of the Cornwall Geological Society, vol. 1, p. 127,
may be consulted; and in the third volume of the same work, p. 166,
will be found an account of the sand bank and submarine forest
existing near the same spot (by Dr. Boase. ED.). Every part of this
parish appears to be intersected with metalliferous veins; some copper
and small quantities of lead have been raised, but tin is the only
metal that has yet proved of importance.
To the above the Editor must add, that Penzance has the good fortune
to possess a geological and mineralogical treasure peculiarly its own.
In the year 1814 Doctor Paris and Mr. Ashurst Majendie began to
institute the Geological Society, and to form a museum. The Society
has flourished far beyond any expectation that could have been
originally formed; and the collection has been enriched by the
liberality of Mr. Carne, Dr. Barham, Mr. Henwood, and others; but,
above all, by Doctor Boase, who has deposited specimens from all parts
of Cornwall, collected on an actual survey extended to each individual
parish. All these specimens are arranged, labelled, and numbered, with
reference to their localities and to his admirable work.
For the general arrangement of the cabinet, with indexes, &c. the
Society and the public are indebted to the ingenuity and industry of
the late Mr. Edward Giddy; and the room of the Cornwall Geological
Society at Penzance may justly be pointed out to scientific strangers
as the object most worthy of their attention throughout the whole
extent of the country.