stratum
is placed, according to Hamilton, "the matter of six eruptions," each
separated from the other by veins of good soil. In these soils Lippi
states that he collected a considerable number of land shells--an
observation which is no doubt correct; for many snails burrow in soft
soils, and some Italian species descend, when they hybernate, to the
depth of five feet and more from the surface. Della Torre also informs
us that there is in one part of this superimposed mass a bed of true
siliceous lava (_lava di pietra dura_); and, as no such current is
believed to have flowed till near one thousand years after the
destruction of Herculaneum, we must conclude, that the origin of a large
part of the covering of Herculaneum was long subsequent to the first
inhumation of the place. That city, as well as Pompeii, was a seaport.
Herculaneum is still very near the shore, but a tract of land, a mile in
length, intervenes between the borders of the Bay of Naples and Pompeii.
In both cases the gain of land is due to the filling up of the bed of
the sea with volcanic matter, and not to elevation by earthquakes, for
there has been no change in the relative level of land and sea. Pompeii
stood on a slight eminence composed of the lavas of the ancient
Vesuvius, and flights of steps led down to the water's edge. The
lowermost of these steps are said to be still on an exact level with the
sea.

_Condition and contents of the buried cities._--After these observations
on the nature of the strata enveloping and surrounding the cities, we
may proceed to consider their internal condition and contents, so far at
least as they offer facts of geological interest. Notwithstanding the
much greater depth at which Herculaneum was buried, it was discovered
before Pompeii, by the accidental circumstance of a well being sunk, in
1713, which came right down upon the theatre, where the statues of
Hercules and Cleopatra were soon found. Whether this city or Pompeii,
both of them founded by Greek colonies, was the more considerable, is
not yet determined; but both are mentioned by ancient authors as among
the seven most flourishing cities in Campania. The walls of Pompeii were
three miles in circumference; but we have, as yet, no certain knowledge
of the dimensions of Herculaneum. In the latter place the theatre alone
is open for inspection; the Forum, Temple of Jupiter, and other
buildings, having been filled up with rubbish as the workmen proceeded,