las; the Veryan series, with Caradoc fossils, is
succeeded in descending order by the Portscatho series, the Falmouth
series and the Mylor series; the lowest Devonian beds represented here
by the Menaccan series, rest unconformably upon these Ordovician beds.
Upper Silurian fossils have been found near Veryan. All these rocks
have been subjected to severe thrusting from the south, consequently
they are much contorted and folded. After this thrusting and folding
had taken place, intrusions of diabase, &c., penetrated the
sedimentary Strata in numerous places, but it was not until
post-Carboniferous times that the granite masses were intruded. The
principal granite masses are those of St Just and Land's End, Penryn,
St Austell and Bodmin Moor. To the granite Cornwall owes much of its
prosperity; it has altered the Killas for some distance around each
mass, and the veins of tin and copper ore, though richest in the
Killas, are evidently genetically related to the granite. The
principal metalliferous districts, Camborne, Redruth, St Just, &c.,
all lie near the granite margins. The china clay and china stone
industry is dependent on the fact that the granite was itself altered
in patches during the later phases of eruptive activity by the agency
of boric and fluoric vapours which kaolinized the felspar of the
granite. Later eruptions produced dykes of quartz-porphyry and other
varieties, all locally called "elvans," which penetrate both the
granite and the Killas. Small patches of Pliocene strata are found at
St Erth and St Agnes Beacon. Blown sand is an important feature at St
Pirran, Lelant, Gwythian and elsewhere, and raised beaches are
frequent round the coast. A characteristic Cornish deposit is the
"Head," an old consolidated scree or talus. Many rare minerals have
been obtained from the mines and much tin ore has been taken from the
river gravels. The river gravel at Carnon has yielded native gold.

_Climate._--The climate of Cornwall is peculiar. Snow seldom lies for
more than a few days, and the winters are less severe than in any other
part of England, the average temperature for January being 34 deg. F. at
Bude and 43.7 deg. at Falmouth. The sea-winds, except in a few sheltered
places, prevent timber trees from attaining to any great size, but the
air is mild, and the lower vegetation, especially in the Penzance
district, is almost southern in its luxuriance.