THIRDLY.

A stone of the same kind with the last, but streaked with numerous,
parallel, slightly tortuous, white lines of the thickness of hairs. These
white lines are more crystalline than the parts between them; and the stone
splits along them: they frequently expand into exceedingly thin cavities,
which are often only just perceptible with a lens. The matter forming the
white lines becomes better crystallised in these cavities, and Professor
Miller was fortunate enough, after several trials, to ascertain that the
white crystals, which are the largest, were of quartz (Professor Miller
informs me that the crystals which he measured had the faces P, z, m of the
figure (147) given by Haidinger in his Translation of Mohs; and he adds,
that it is remarkable, that none of them had the slightest trace of faces r
of the regular six-sided prism.), and that the minute green transparent
needles were augite, or, as they would more generally be called, diopside:
besides these crystals, there are some minute, dark specks without a trace
of crystalline, and some fine, white, granular, crystalline matter which is
probably feldspar. Minute fragments of this rock are easily fusible.

FOURTHLY.

A compact crystalline rock, banded in straight lines with innumerable
layers of white and grey shades of colour, varying in width from the
thirtieth to the two-hundredth of an inch; these layers seem to be composed
chiefly of feldspar, and they contain numerous perfect crystals of glassy
feldspar, which are placed lengthways; they are also thickly studded with
microscopically minute, amorphous, black specks, which are placed in rows,
either standing separately, or more frequently united, two or three or
several together, into black lines, thinner than a hair. When a small