406 REPORT—1 890. 
On the irregularly eroded surface of the yellow tuff we find deposits 
of a great number of large boulders and pebbles of the same tuff, torn 
by the action of the sea from the shore-line of reefs. These pebble beds 
are in fact the shore-line equivalents of the Pozzolana sand and rounded 
lapilli of the Starza, which, where now seen in section, were deposited 
farther from the shore. 
Subsequent to the erosion of these ancient tuff reefs, and the deposi- 
tion around them of conglomerates, gravels, and finer materials, a vent 
opened at the site of Monte Olibano, and probably ata point now traversed 
by the strada 8. Gennaro. From this mouth issued several trachyte lava 
streams, one of which, on account of its great viscidity, stopped a short 
distance from its point of issue, piling itself up and accumulating in the 
place where we now see it cut into chiefly by man’s hand, and forming 
great irregular cliffs in the different stone quarries on the Pozzuoli road. 
Before this lava flowed out, a great quantity of the fused rock was 
ejected by the violence of the explosions in a fragmentary state as scori 
and pieces of scoriaceous trachyte, which falling formed very irregular 
strata often several metres thick. The contact of these pieces of hot rock 
with the subjacent pozzolana and tuff has produced in most places the 
usual characteristic red coloration which indicates that the land had 
then risen very considerably, for had the hot scoriz fallen into the water 
they would have been cooled before they reached the bottom, and could 
not then have produced the characteristic coloration. 
At the lowest point where scoriz are in contact with older deposits, 
and close to the Pozzuoli road, the reddening is absent, and therefore we 
must conclude that although elevation had gone on it had not yet attained 
that level. 
Probably there were several eruptions from Monte Olibano, though it 
is difficult to determine how many, for between the bands of trachytic 
scoriz beds of re-sorted tuff occur which probably required a certain time 
to be deposited. 
Some traces of the crater formed during the principal explosions are 
to be seen to the right of the upper road going to 8. Gennaro and Pozznoli 
and facing the entrance to the Fondo Sarno. To the left we see the 
trachyte in the form of a gigantic mamelon over the side of the vent, and 
from which is prolonged the short, dumpy lava stream that probably 
flowed over the lower edge of the crater towards the sea. 
The mass of trachyte which in part constitutes the inner south de- 
clivity of the actual crater of the Solfatara is a trachyte lava which 
flowed to the N. or N.W. at a date corresponding to the first eruptions 
of the voleano of Monte Olibano, and the masses and altered breccias, &c., 
which now form the steep boundaries of the solfatara crater and posterior 
to the trachyte are due to later eruptions of Monte Olibano and the actual 
Solfatara. It was also from here that issued those streams seen in the 
cliff behind the Bath establishment of Subveni Homini, which are, there- 
fore, probably more ancient than the trachyte of the Cava Regia, 
Mura, &c. 
The mass of trachyte of the Solfatara crater wall might also be a dyke, 
but it seems impossible for it to have so nearly reached the surface without 
overflowing. The actual crater of the Solfatara was produced by an explo- 
sion at a posterior epoch, the material from which accumulated in great 
deposits upon all the anterior formation, and considerably changed the 
preceding configuration of the surface. 
