sland, and landed under the two pitchstone veins of
Eigg, so generally known among mineralogists, and of which specimens may
be found in so many cabinets. They occur in an earthy, greenish-black
amygdaloid, which forms a range of sea-cliffs varying in height from
thirty to fifty feet, and that, from their sad hue and dull fracture,
seem to absorb the light; while the veins themselves, bright and
glistening, glitter in the sun, as if they were streams of water
traversing the face of the rock. The first impression they imparted, in
viewing them from the boat, was, that the inclosing mass was a pitch
caldron, rather of the roughest and largest, and much begrimmed by soot,
that had cracked to the heat, and that the fluid pitch was forcing its
way outwards through the rents. The veins expand and contract, here
diminishing to a strip a few inches across, there widening into a
comparatively broad belt, some two or three feet over; and, as well
described by M'Culloch, we find the inclosed pitchstone changing in
color, and assuming a lighter or darker hue, as it nears the edge or
recedes from it. In the centre it is of a dull olive green, passing
gradually into blue, which in turn deepens into black; and it is exactly
at the point of contact with the earthy amygdaloid that the black is
most intense, and the fracture of the stone glassiest and brightest. I
was lucky enough to detach a specimen, which, though scarce four inches
across, exhibits the three colors characteristic of the vein,--its bar
of olive green on the one side, of intense black on the other, and of
blue, like that of imperfectly fused bottle-glass, in the centre. This
curious rock,--so nearly akin in composition and appearance to
obsidian,--a mineral which, in its dense form, closely resembles the
coarse dark-colored glass of which common bottles are made, and which,
in its lighter form, exists as pumice,--constitutes one of the links
that connect the trap with the unequivocally volcanic rocks. The one
mineral may be seen beside smoking crater, as in the Lipari Isles,
passing into pumice; while the other may be converted into a substance
almost identical with pumice, by the chemist. "It is stated by the
Honorable George Knox, of Dublin," says Mr. Robert Allan, in his
valuable mineralogical work, "that the pitchstone of Newry, on being
exposed to a high temperature, loses its bitumen and water, and is
converted into a light substance in every respect resembling pumi