defied, and the
substances in solution are crystallised in bands of equal thickness on
every side of the cell. It would require a course of lectures longer
than these (I have a great mind,--you have behaved so saucily--to stay
and give them) to describe to you the phenomena of this kind, in agates
and chalcedonies only;--nay, there is a single sarcophagus in the
British Museum, covered with grand sculpture of the 18th dynasty, which
contains in the magnificent breccia (agates and jaspers imbedded in
porphyry), out of which it is hewn, material for the thought of years;
and record of the earth-sorrow of ages in comparison with the duration
of which, the Egyptian letters tell us but the history of the evening
and morning of a day.

Agates, I think, of all stones, confess most of their past history; but
all crystallisation goes on under, and partly records, circumstances of
this kind--circumstances of infinite variety, but always involving
difficulty, interruption, and change of condition at different times.
Observe, first, you have the whole mass of the rock in motion, either
contracting itself, and so gradually widening the cracks; or being
compressed, and thereby closing them, and crushing their edges;--and, if
one part of its substance be softer, at the given temperature, than
another, probably squeezing that softer substance out into the veins.
Then the veins themselves, when the rock leaves them open by its
contraction, act with various power of suction upon its substance;--by
capillary attraction when they are fine,--by that of pure vacuity when
they are larger, or by changes in the constitution and condensation of
the mixed gases with which they have been originally filled. Those gases
themselves may be supplied in all variation of volume and power from
below; or, slowly, by the decomposition of the rocks themselves; and, at
changing temperatures, must exert relatively changing forces of
decomposition and combination on the walls of the veins they fill; while
water, at every degree of heat and pressure (from beds of everlasting
ice, alternate with cliffs of native rock, to volumes of red hot, or
white hot, steam), congeals, and drips, and throbs, and thrills, from
crag to crag; and breathes from pulse to pulse of foaming or fiery
arteries, whose beating is felt through chains of the great islands of
the Indian seas, as your own pulses lift your bracelets, and makes whole
kingdoms of the world quiver in deadly eart