combined with the heavy expense of transport, prevents it from
being worked.
A very large variety of clays exists in many places between the
lava beds and on the high land. Several of them are of a pure
white, which leads to the idea that some value might attacli to them
as material for the manufacture of porcelain. They have, however,
been pronounced valueless for such a purpose. In the year 1868, a
large and carefully-made collection of them was tested by Mr. John
Mortlock, of Oxford Street, London, and he reported that trials
made with them showed that, without an exception, they all contained
more or less iron, which rendered them totally unfit for
potter’s purposes.
Such rocks and minerals as are found chiefly to occur are,
together with localities and particulars, as follows :—
Dense, very finely crystalline basalt.
Ditto, containing disseminated crystals of augite and olivine—
s.g. 2-83 to 313.
Ditto, with iron chrysolite.
Dense basalt, with few cavities containing sea water—s . g . 2-S4;
James’ Valley.
Highly scoriaceous lava.
Amygdaloidal lava.
Phonolite or clinkstone ; great Lot dike, Ass’s Bars, &c.
Numerous varieties of felspathic lavas, varying from basalt and
greystone to trachyte—s . g . 2’61.
Volcanic bombs or pear-shaped masses of lava.
Porphyritic basalt, containing crystals of felspar, augite, &c.—
Dike in Turk’s Cap Valley.
Amygdaloidal greystone, containing embedded augite and iron
chrysolite, some of the cavities being lined with very minute,
brilliant, and perfect cubic crystals of zeolite, probably
chabazite.
Amygdaloidal greystone, the cavities filled with zeolite in very
small boitroidal masses, composed of extremely minute
radiating fibrous crystals, probably natrolite.
Amygdaloidal lava filled with perfectly spherical, very minute
cavities, coated on the inside with a thin layer of zeolitic
mineral.
Cellular Lava.—Many varieties.
Trachyte.—s.g. 2*523.
Ditto, passing into white clay; below Bamboo Hedge, at
Ladder Hill, &c.—s.g. 2*75.
Lamelliferous greystone dike from immediate proximity to augite
and other dikes; Manatee Bay.
Laterite.—Various colours and degrees of hardness, between beds
of Lava.
Volcanic tufa, between layers of lava.
Volcanic breccia or pudding stone ; Ladder Hill, &c.
Volcanic scoriaceous agglomerate.
Compressed tufaceous rock.
Compressed tufaceous rock, coloured red by oxide of iron, and
containing augite, &c.; Bed Quarry, Woodlands, Bock
. Cottage, Buperts; a compact variety, much hardened by
plutonic action and pressure between the thick layers of
lava, is largely used as a dressed stone for building purposes.
A coating of mortar on the exposed face preserves
it from atmospheric action. The basalts and harder rocks
are used chiefly for rubble building and for macadamizing
roads.
Agglomerate rocks formed of masses of scorise and volcanic ashes
lying between the beds of laterite and lava.
Porphyritic lava, containing disseminated crystals of carbonate
of lime; Holdfast Tom.
Volcanic scoria and pumice ; High Knoll.
Volcanic ashes.
Fossiliferous-like masses of scoriae; High Knoll.
Augite rock; Turk’s Cap, Manatee Bay, &c.
Siliceous rock—Flint, coloured by oxide of iron, chiefly in pebbles
on seashore at Manatee Bay.—s.g. 2-60.
Dolerite, containing disseminated augite and chrysolite, partially
amygdaloidal and zeolitic. The cavities containing crystallized
chabazite.—s. g.2'85. Dike on crater edge above Thompson’s
Wood.
Bed porphyritic lava from dike at Prosperous Bay.
Trachyte dikes, very laminated, exhibiting, through colouring
by oxide of iron, a false appearance of stratification.—s.g.
2'64. Prosperous Bay.