separate:  and you see the rents are now all filled up with the sanguine paste, full of the broken pieces of the rock; the paste itself seems to have been half melted, and partly to have also melted the edge of the fragments it contains, and then to have crystallized with them, and round them.  And the brecciated agate I first showed you contains exactly the same phenomena; a zoned crystallization going on amidst the cemented fragments, partly altering the structure of those fragments themselves, and subject to continual change, either in the intensity of its own power, or in the nature of the materials submitted to it;—­so that, at one time, gravity acts upon them, and disposes them in horizontal layers, or causes them to droop in stalactites; and at another, gravity is entirely defied, and the substances in solution are crystallized 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 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 crystallization 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,