252 
THE MEDITERRANEAN NATURALIST 
Possibly we may be shortly able to clear up this 1 
difficulty, a most unexpected discovery having ! 
been recently made in the very heart of Naples, 1 
and one to which I am led to attribute considerable 
geological importance. 
At the present time a large main sewage drain 
is being driven through the soft tufa rock from 
the South-eastern part of the city to the vicinity 
of Fuorigrotta, outside the city to the north-west 
under the Villa Montfort, at the lower end of the 
Parco Gripo, close to the Corso Vittorio Emanuele 
the sewer is situated at the level of 13m. 70cm. 
above the sea; 250 farther north, close to the new 
International Hospital, it is slightly more than 13m. 
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 40 m. of it having 
been already bored thr ough, 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 persons 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-gray or 
bluish colour, and equal to the hardest and most 
compact kind found in any part of the Phlegragan 
Fields, being of identical structure to some met 
with at Pozzuoli, and like it enclosing small crystals 
of sanidina, 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 midle 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. Guisti, 
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 contain- 
ing large fragmentary pieces of undecomposed 
pumice stone, a variety peculiar to this neighbour- 
hood; 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 block 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 simultaneous origin to the 
quaternary though it cannot yet be decided 
whether it ever reached the surface, or whether 
there were not some lateral veins, or blind dyke, 
which forced its way up those the already existing 
tufa. The subject offers much interest, and I hope 
sistency, or is of any economic value. 
It will be immediately observed, on the most 
superficial examination, how remarkably irregular 
the bedding of even the thickest strata is, as they 
rapidly thin out, and often disappear a^togethe.. 
to be replaced by others of very different litholo- 
gical structure. As if to add to such irregularity, 
the dip of the beds is very varying and inconstant; 
in one spot it appears to be horizontal, a few yards 
beyond it is not unfrequently undulating, and 
further on inclined at a high angle— suggesting 
the probabity of upheaval and giving way of the 
strata through local volcanic agency, exerted at a 
very slight depth below the surface and frequently 
repeated. 
In quarying the tufa as a building material, 
invaluable on account of its remarkable cheapness 
5 pieces of a roughly paralellopipidal shape together 
measuring about two cubic feet, being worth 
only a franc — the greatest difference is found 
to exist in the coefficient of resistence to pres- 
sure and crushing strain, according to the lo- 
cality and series of beds whence the stone is 
procured. One point, however, is found in com- 
mon; it was all bedded as a litoral deposit and in 
shallow sea water, and in confirmation of this fact 
large oyster shells may sometimes be me with in 
it. Lead— gray volcanic tufa is largely developed 
at the southern entrance to the Bay of Naples, 
around Sorrento, but it is no where to be met with 
on the north sida of Vesuvius, or beyond the 
region I am describing in the direction of Pozzuoli 
or in the islands of Procida or Ischia. 
Topographically the tufa hills of Posillipo and 
Naples continue in the direction of the old Ca- 
maldoli convent, in which neighbourhood scoria- 
ceous and other lava is largely developed: in other 
directions these hills have no connection with any 
others for towards Vesuvius and in the direction 
