[ 33 3 
made Its appearance at Naples, before it fpread its 
contagion over the other parts of Europe. 
Virgil and other ancient authors fay, that birds 
could not fly with fafety over the lake of Avernus, 
but that they fell therein ; a circumftance favouring 
my opinion that this was once the mouth of a vol- 
cano. The vapour of the fulphur and other minerals 
mufl: undoubtedly have been more powerful the 
nearer we go back to the time of the explofion of 
the volcano ; and I am convinced that there are ftill 
fome remains of thofe vapours upon this lake, as I 
have obferved there are very feldom any water fowl 
upon it ; and that when they do go there, it is but 
for a fhort time, whilft all the other lakes in the 
neighbourhood are conftantly covered with them, in 
the winter feafon. Upon mount Vefuvius, in the 
year 1766, during an eruption, when the air was 
impregnated with noxious vapours, I have myfelf 
picked up dead birds frequently. 
The caflile of Baia ftands upon a confiderable 
eriiinence, compofed of the ufual tufa and flrata of 
pumice and alhes, from which I concluded I fhould ' 
find fome remains of the craters from whence the 
matter iflhed 5 accordingly, having afcended the hill, 
I foon difcovered two very vifible craters, juft behind 
the caftle. 
The lake called the Mare morto was alfo, moft 
probably, the crater from whence iflhed the materials 
which formed the Promontory of Mifenum, and the 
high grounds around this lake. Under the ruins of 
an ancient building near the point of Mifenum, in a 
vault, there is a vapour, or mofete. exactly fimilar in 
VoL. LXI. F its 
