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The mountains at the hack of Caferta are mofily of 
a fort of lime -Rone, and very different from thofe 
.formed by hre; though Signior Van Vitelli, the ce- 
lebrated architedt, has affured me, that in the cutting 
of the famous aquedudl of Caferta through thefe 
mountains, he met with fome foils, that liad been 
evidently formed by fubterraneous fires. The high 
grounds which extend from Cafiel-a-Mare to the 
point of Minerva towards the ifland of Caprea, and 
from the promontory that divides the bay of Naples 
from that of Salerno, are of lime Rone. The plain 
of Sorrento, that is bounded by thefe high grounds, 
beginning at the village of Vico, and ending at that 
of Mafia, is wholly compofed of the fame lort of tufa 
as that about Naples, except that the cinder or pumice 
Rones intermixed in it are larger than in the Naples 
tufa. I conceive then that there has been an ex'- 
plofion in this fpot from the bottom of the fea. This 
plain, as I have remarked to be the cafe with all foils 
produced by fubterraneous fire, is extremely fertile j 
whilR the ground about it, being of another nature, 
is not fo. The ifiand of Caprea does not fiiew any 
figns of having been formed by fubterraneous fire, 
but is of the fame nature as the high grounds laR 
mentioned, from which it has been probably detached 
by earthquakes, or the violence of the waves. Ro- 
vigliano, an ifiand, or rather a rock in the bay of 
CaRel-a-Mare, is likewife of lime Rone, and feems 
to have belonged to the original mountains in its 
neighbourhood : in fome of thefe mountains there 
are alfo petrified fifii and fofiil Riel Is, which I never 
have found in the mountains, which I fuppofe to 
have been formed by explofion. 
You 
