owing to the difficulty of removing it from so great a depth below
ground. Even the theatre is only seen by torch-light, and the most
interesting information, perhaps, which the geologist obtains there, is
the continual formation of stalactite in the galleries cut through the
tuff; for there is a constant percolation of water charged with
carbonate of lime mixed with a small portion of magnesia. Such mineral
waters must, in the course of time, create great changes in many rocks;
especially in lavas, the pores of which they may fill with calcareous
spar, so as to convert them into amygdaloids. Some geologists,
therefore, are unreasonable when they expect that volcanic rocks of
remote eras should accord precisely with those of modern date; since it
is obvious that many of those produced in our own time will not long
retain the same aspect and internal composition.

Both at Herculaneum and Pompeii, temples have been found with
inscriptions commemorating the rebuilding of the edifices after they had
been thrown down by an earthquake.[555] This earthquake happened in the
reign of Nero, sixteen years before the cities were overwhelmed. In
Pompeii, one-fourth of which is now laid open to the day, both the
public and private buildings bear testimony to the catastrophe. The
walls are rent, and in many places traversed by fissures still open.
Columns are lying on the ground only half hewn from huge blocks of
travertin, and the temple for which they were designed is seen half
repaired. In some few places the pavement had sunk in, but in general it
was undisturbed, consisting of large irregular flags of lava joined
neatly together, in which the carriage wheels have often worn ruts an
inch and a half deep. In the wider streets, the ruts are numerous and
irregular; in the narrower, there are only two, one on each side, which
are very conspicuous. It is impossible not to look with some interest
even on these ruts, which were worn by chariot wheels more than
seventeen centuries ago; and, independently of their antiquity, it is
remarkable to see such deep incisions so continuous in a stone of great
hardness.

_Small number of skeletons._--A very small number of skeletons have been
discovered in either city; and it is clear that most of the inhabitants
not only found time to escape, but also to carry with them the principal
part of their valuable effects. In the barracks at Pompeii were the
skeletons of two soldiers chained to the stock