of different horizontal beds of tuff and lapilli, for the
most part thin, and subdivided into very fine layers. I observed the
following section near the amphitheatre, in November, 1828--(descending
series):--

Feet Inches.

1. Black sparkling sand from the eruption of 1822,
containing minute regularly formed crystals of augite
and tourmaline 0 2-1/2

2. Vegetable mould 3 0

3. Brown incoherent tuff, full of _pisolitic globules_
in layers, from half an inch to three inches in
thickness 1 6

4. Small scoriae and white lapilli 0 3

5. Brown earthy tuff, with numerous pisolitic globules 0 9

6. Brown earthy tuff, with lapilli divided into layers 4 0

7. Layer of whitish lapilli 0 1

8. Gray solid tuff 0 3

9. Pumice and white lapilli 0 3
-------
10 3-1/2
-------

Many of the ashes in these beds are vitrified, and harsh to the touch.
Crystals of leucite, both fresh and farinaceous, have been found
intermixed.[549] The depth of the bed of ashes above the houses is
variable, but seldom exceeds twelve or fourteen feet, and it is said
that the higher part of the amphitheatre always projected above the
surface; though if this were the case, it seems inexplicable that the
city should never have been discovered till the year 1750. It will be
observed in the above section that two of the brown, half-consolidated
tuffs are filled with small pisolitic globules. This circumstance is not
alluded to in the animated controversy which the Royal Academy of Naples
maintained with one of their members, Signor Lippi, as to the origin of
the strata incumbent on Pompeii. The mode of aggregation of these
globules has been fully explained by Mr. Scrope, who saw them formed in
great numbers in 1822, by rain falling during the eruption on fine
volcanic sand, and sometimes also produced like hail in the air, by the
mutual attraction of the minutest particles of fine damp