518 CARBONIFEROUS VOLCANIC ROCKS OF THE FIRTH OF FORTH BASIN. 
Fig. 
6. Pikrite, Blackburn, Bathgate—This rock consists mainly of serpentine of very 
varied texture and colour, containing numerous tolerably well-marked forms of the 
original olivine, and occasionally reticulated portions in which the distinct polarisa- 
tion of the latter mineral may still be detected. The augite occurs in large admirably 
fresh well-defined crystals of a fine claret colour in thin slices. It often encloses 
erystals of olivine. A few fragments of magnetite or titaniferous iron are shown 
with here and there traces of their having been oxidised and hydrated into the brown 
hydrous peroxide of iron. (20 diameters.) See p. 504. 
PuaTE XII, 
Fig. 
Fig. 
7. Porphyrite, Pencraig Quarry, Garlton Hills—A rock, consisting mainly of 
triclinic felspar, in small ill-defined prisms, with abundant grains, shreds, and crystals 
of magnetite and occasional augite. Traces of the oxidation and hydration of the 
iron are seen in the brown spots. (20 diameters.) See p. 508. 
. 8. Same as fig. 7, seen between crossed Nicol prisms. The ground-mass interposed 
between the felspar crystals now appears clouded, being partly quite dark and partly 
admitting a milky blue light. (20 diameters.) 
..9. Felsite, Volcanic Neck, Shore at Largo, Fife—A finely granular felsitic ground- 
mass, with a kind of perlitic structure. In certain portions of the rock between the 
wavy lines of closer aggregation in the ground-mass, clear crystals of samidine and 
granules of quartz, with fluid cavities, are enclosed. (20 diameters.) See p. 510, 
.10, Tuff, Kilmundy Hill, Burntisland.—An ageregate of irregular fragments of different 
lavas. The largest of these here shown consists of a bright green serpentinous 
substance, exceedingly cellular, and containing occasional plagioclase crystals and 
microlites (see p. 513). Between the lapilli much brown opaque decomposed matter 
is diffused. 
11. Veins of Dolerite traversing altered Shale, Salisbury Crags, Edinburgh.—The 
dolerite is exceedingly close-grained, becoming here and there, especially along the 
edges, quite black and opaque. At the lower portion of the field it is seen to be full of 
microlites of titaniferous iron or magnetite. It encloses numerous perfectly formed 
prisms of triclinic felspar. The shale consists of a porcellanised base, with clear 
round granules of quartz. See p. 497. 
. 12. Dolerite from edge of sheet near contact with sandstone, Gartness, Airdrie— 
The large prisms of triclinic felspar and patches of titaniferous iron are the most con- 
spicuous features. No augite appears, its place being probably taken by some of the 
abundantly diffused green decomposition products, The remarkable forms originally 
assumed by the iron, and preserved in those parts of rock which have been rapidly 
congealed, are shown in this drawing. See p. 496 e¢ seg. 
‘in 
