[ 49 ]■ 
an exifting volcano, is plain, from the ancienf cur- 
rents of lava, that are ftill to be traced from its crater 
to the fea, from the ftrata of pumice and erupted 
matter, of which its cone, in common with thofe of 
all other volcanos, is compofed, and from the tefti- 
inony of many ancient authors. Its cone in many 
parts has been calcined, and is ftill calcining, by the 
hot vapours that are continually iffuing forth through 
its pores, and its nature is totally changed by this 
chemical proeds of nature. In the hollow way, 
where I uiade thefe remarks, you fee the different 
ffrata of erupted matter, that compofe the cone in 
fome places perfedly calcined,’ in others not, accord- 
ing as the vapours have found means to infinuate 
themfelves more or lefs. 
A hollow way cut by the rains on the back of the 
mountain, on which part of Naples is fituated, to- 
wards Capo di China, diews that the mountain is 
compofed of ffrata of erupted matter, among which 
are large maffes of bitumen, in which its former 
ffate of fluidity is very vifible. Here it was I dlf- 
covered that pumice ftone is produced from bitu- 
men, which 1 believe has not yet been remarked. 
Some fpecimens ffiew evidently the gradual procefs 
from bitumen to pumice; and you will obferve that 
the cryffalline vitrifications, that are vifible in the 
bitumen, fuffer no alteration, but rem-ain in the fame 
ffate in the perfed pumice as in the bitumen. 
In a piece of ffratum, calcined from the out- 
fide of the Solfaterra, ahe form and texture of 
the pumice ffones is very difcernible. In feveral 
parts of the outfide cone, this calcining operation is 
ffill carried on by the exhalation of conffant very hot 
VoL. LXI. H and 
