86 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
seemed to descend and cover the whole ocean [it probably was the 
north wind, or tramontana| as it certainly hid the island of Capri 
and the promontory of Misenum. Soon after they were enveloped 
in darkness, and a cloud of ashes.” “ Atlast this dreadful darkness 
was dissipated by degrees, like a cloud of smoke; and the real day 
returned, and soon the sun appeared, though very faimtly, as when 
an eclipse is coming on. Every object that presented itself to our 
eyes (which were extremely weakened) seemed changed, being 
covered over with white ashes as with a deep snow.” From this 
we learn that the latter part of the eruption was accompanied by 
the ejection of ashes. 
The size of some of the fragments that fell in Pompeii was occa- 
sionally considerable. Sir W. Hamilton mentions* some weighing 
eight pounds, but remarks that they decrease as we proceed towards 
Castellamare, a fact we should expect. Large blocks of pumice and 
lava are commonly to be met with weighing five or six pounds. 
It will be remarked that, in general characters, this Plinian de- 
posit resembles very much that described under the heading PHasE 
VI., Pertod 4; so much so in fact as to lead one to correlate them 
together. We have for instance :— ; 
lst. The pumice capable of two analogous subdivisions quite or 
at least almost similar. 
2nd. The deposit in appearance terminating with a pisolitic ash- 
bed. 
drd. The similarities in the accessory and accidental components 
of the ejectamenta, viz. leucilitic lapilli; and the great variety of 
sedimentary and metamorphic erratics. 
4th. The opinions of so many eminent and careful observers as 
Breislak, Scrope, Daubeny, Scacchi, and a host of others. 
Indeed so striking is the resemblance, that up to quite a recent 
date I fully believed the same myself. When, however, the micro- 
scope revealed the enormous abundance of leucite in the Plinian, 
and its practically total absence in pre-Plinian pumice, with other 
details of minute structure, and these were superadded to stratigra- 
phical reasons, such preconceived ideas were obliged to give way. 
Neither was the conclusion based on only one or two preparations, 
but sections were prepared from every conceivable variety, and of 
pumice from many localities. 
At the Canale di Arena the deposits of Paasr VI., Period 4 can 
be easily recognized, its pisolitic division being well developed. 
Above this and distinctly superimposed upon it, is a bed of pumice 
in all respects identical with that covering Pompeii, and with regard 
to which there seems to be little doubt that they both belong to 
the same eruption. 
In the Lagno di Troechia, in a section of the valley side at a certain 
height, may be seen the entombed ruin of a Roman villa reposing on 
deposits of the pre-Plinian eruption, the pumice of which has been 
used as a mortar-making material, proving the house to be posterior 
to that eruption. I have obtained a number of potsherds, bits of 
* ~Campi Phlegrei.’ 
