The western part of this parish rests on granite, which is generally
coarse-grained and crystalline, often with large porphyritic crystals
of felspar; here and there it contains beds of porphyry (elvan
courses), and also of shorl rock, sometimes in masses, but more
frequently in the form of large and irregular veins. This granite has
been productive of metallic ores, and more particularly of tin. The
eastern part is composed of rocks belonging to the porphyritic series.
The principal varieties are felspar rock, both massive and schistose,
and green-stone. The soil derived from these rocks, as is often the
case near granite, is on some spots very fertile. Some land near the
entrance into Hayle is covered with testaceous sand, so common in the
vicinity of all the bays and inlets of the sea on the north coast of
Cornwall, and which, whenever it is unprotected by vegetation, is
drifted by the winds over the uncultivated lands. Nature has pointed
out the remedy for this evil to be the diffusion and increase of
arenaceous plants.
THE EDITOR.――Whele Reath, a mine on the extreme western border of this
parish, where it joins Towednack, has proved more productive of tin
than any other mine except Whele Vor; and it has been prosecuted to a
depth unexampled till within these few years, even in mines of copper.
At the other extremity of the parish, near the sea-shore, both copper
and tin have been found in the belt of green stone which generally
interposes between the granite and the sea-shore.