Chev. W. P. Jervis— Volcano of Mergillina. 200 
the new International Hospital, it is slightly more than 18m. above 
the sea-level; the surface of the ground above being respectively 
100m. and 65m. at the points alluded to. Just under the Villa 
Montfort trachyte rock was met with, 40m. of it having been already 
bored through, while at the surface not a trace of such rock was 
ever suspected to exist, volcanic tufa alone being seen; nor did it 
ever come under any person’s observation that trachyte should 
anywhere be met with in the tufa hills I am describing. The 
trachyte, which I have carefully examined, is of a dark lead-grey 
or bluish colour, and equal to the hardest and most compact kind 
found in any part of the Phlegrean Fields, being identical in 
structure to some met with at Pozzuoli, and like it enclosing small 
erystals of sanidine or glassy felspar. Attiguous to the trachyte, 
and for a certain distance from it to the south-east, the tufa is very 
pumiceous, and large loose blocks of trachyte of a yellowish tinge 
are to be found imbedded in the midst of the tufa, from which they 
do not essentially differ in colour. Sometimes the tufa adheres 
firmly to the trachyte, which might lead us to suppose that the 
latter must have fallen on the surface of the tufa before it had had 
time to be perfectly cooled. M. Giusti, the engineer in charge of 
the works at this point, kindly gave me the following data. After 
leaving the ordinary yellow tufa common to these hills, some beds 
of good yellow tufa were pierced, then rather clayey tufa; after 
which dark- yellow tufa containing large fragmentary pieces of 
undecomposed pumice, a variety peculiar to this neighbourhood ; 
then a gentle synclinal of white tufa, each of these several beds 
being but a few metres in thickness. After this followed 30m. of 
pumiceous tufa, containing large loose blocks of trachyte, followed 
by the trachyte rock in situ above alluded to. 
Have we not here the evidence of the existence of a volcanic 
eruption of Quaternary age, though it cannot yet be decided whether 
it ever reached the surface, or whether there were not some lateral 
veins, or a blind dyke, which forced its way up through the already 
existing tufa. The subject offers much interest, and I hope some 
day to be able to communicate further information regarding it. I 
am led to conclude that the central crater of this volcano must have 
been situated within a mile of the present coast-line in a spot now 
occupied by deep water, the cone having subsided since the Quaternary 
period. Should my conjecture be found admissible we might apply 
the name of “ Mergellina volcano” to this trachytic ejection, and 
we might then be authorized to regard the tufa hiils of Naples and 
Posillipo as having had their origin thence. Both the trachyte 
and the yellow tufa are rocks common to all the volcanoes of the 
Phlegrzan Fields and the neighbouring islands, while leucitic rocks 
characterize Monte Somma, and augite and leucite Vesuvian rocks. 
While speaking of the neighbourhood of Naples I may just give 
the results of a few very careful observations I made this spring 
of the temperature of several thermal springs and fumaroles, and 
compare them with former studies. 
Casamicicola, Island of Ischia.—Acqua del Gurgitello, February 
1869, 84°. c. (Jervis) ; 10th May, 1892, 84°. c. (Jervis). 
