102 H. J. JOHNSTON-LAVIS ON THE GEOLOGY 
This deposit is of the most varied type, ranging from the coarsest 
breccia to the finest ash, or from a collection of pumice to a bed 
of rounded leucilitic lapilli. The arrangement may show great 
false-bedding or long parallel strata, which are often most mislead- 
ing. In the Valloni Grande and di Pollena one may recognize 
the Plinian pumice forming the lower part of these deposits, but 
having the appearance of having been transported and rounded 
by water, so as to resemble very much some of the tufa over Hercu- 
laneum. | 
This more or less variable agglomerate of different materials is 
usually broken near its middle by the thick bed of black pumiceous 
scoria of Puasr VII. It is occasionally possible to recognize rem- 
nants of products from other eruptions of the same PHAsE. 
Any one who follows the road that winds round the foot of the 
mountain from St. Giovanni di Teducio to St. Anastasia will be 
strongly impressed by the wayside sections. ‘These are rarely more 
than two metres in thickness, the upper third being disturbed vege- 
table soil, whilst the lower limit is not visible. Beneath the top 
soil are fine undulating lamine, which may be traced for very 
long distances. As we enter the town of St. Anastasia, there 
may be seen a series of alternations of fine dusty tufa with beds 
of coarser materials, some remarkably crumpled or undulating in 
arrangement. 
No one seeing these beds would regard them otherwise than as the 
result of gradual aqueous deposition. I have examined them over ~ 
and over again, with the hope of finding some organic remains, but 
without a shadow of success ; nevertheless their remarkable strati- 
graphical characters certainly seem to make one require other means 
than simple alluvial deposition. 
In a few cases it has been possible to show that these deposits 
immediately follow the end of Pass VI. It is therefore possible 
that some very important changes of level took place between 
the last prehistoric outburst and the Plinian eruption. Of this 
no historic evidence is known to us, and therefore we are left 
without any sound facts from which we could safely arrive at 
a conclusion either way. It is, however, to be hoped that some- 
thing will crop up to decide so interesting a question, such as the 
finding of organic remains or antiquities. 
If we should really find these tufas to be of marine origin, they 
will prove that, at no distant epoch, Vesuvius was an island, and 
that almost, if not really, in historic times the sea surrounded the 
greater part of its base. 
Let us now return to those deposits of the same age that are found 
at a higher level, and of whose origin there is no doubt. They are, 
as already pointed out, most variable in composition, necessarily 
depending on the rocks from which they were derived. So much 
is this the case that, where the origin has not been mixed, the 
re-sorted lapilli or pumice may easily mislead an observer into error 
and trouble by showing an apparent reversal of order; and there are 
examples that require the most careful examination. When these 
