curiously formed veins have, I believe, been formed by siliceous matter
being subsequently segregated. But my chief reason for believing that these
soft earthy stones, with their extraneous fragments, are not of sedimentary
origin, is the extreme improbability of crystals of feldspar, black
microscopical specks, and small stains of a darker colour occurring in the
same proportional numbers in an aqueous deposit, and in masses of solid
trachyte. Moreover, as I have remarked, the microscope occasionally reveals
a crystalline structure in the apparently earthy basis. On the other hand,
the partial decomposition of such great masses of trachyte, forming whole
mountains, is undoubtedly a circumstance of not easy explanation.

VEINS IN THE EARTHY TRACHYTIC MASSES.

These veins are extraordinarily numerous, intersecting in the most
complicated manner both coloured varieties of the earthy trachyte: they are
best seen on the flanks of the "Crater of the old volcano." They contain
crystals of glassy feldspar, black microscopical specks and little dark
stains, precisely as in the surrounding rock; but the basis is very
different, being exceedingly hard, compact, somewhat brittle, and of rather
less easy fusibility. The veins vary much, and suddenly, from the tenth of
an inch to one inch in thickness; they often thin out, not only on their
edges, but in their central parts, thus leaving round, irregular apertures;
their surfaces are rugged. They are inclined at every possible angle with
the horizon, or are horizontal; they are generally curvilinear, and often
interbranch one with another. From their hardness they withstand
weathering, and projecting two or three feet above the ground, they
occasionally extend some yards in length; these plate-like veins, when
struck, emit a sound, almost like that of a drum, and they may be
distinctly seen to vibrate; their fragments, which are strewed on the
ground, clatter like pieces of iron when knocked against each other. They