76 
ST. SELENA. 
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 attach 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 con- 
tained 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 3T3. 
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 Ears, &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. 
