[ 7 -] 
hood of Puzzole, where explofions have been fre- 
quent. The gradual decreafe in the fize and quan- 
tity of the erupted matter in the flratum above- 
mentioned, from Pompeii to Caftle-a-Mare, is very 
vifible: at Pompeii, as I faid before, I have found 
them of eight pounds weight, when at Caflle-a-Mare 
the largeft do not weigh an ounce. 
The matter which covers the ancient town of 
He rculaneum is not the produce of one eruption onlyj 
for there are evident marks that the matter of fix 
eruptions has taken its courfe over that which lies 
immediately above the town, and was the caufe of 
its deftrudlion. Thefe firata are either of lava or 
burnt matter, with veins of good foil between them. 
The firatum of erupted matter that immediately 
covers the town, and with which the theatre and 
moft of the houfes were filled, is not of that foul 
vitrified matter, called lava, but of a fort of foft 
flone, compofed of pumice, aflies, and burnt matter. 
It is exactly of the fame nature with what is called 
here the Naples flone ; the Italians diftinguifli it by 
the name of /u/a, and it is in general ufe for build- 
ing. Its colour is ufually that of our free ftone, but 
fometimes tinged with grey, green, and yellow; and 
the pumice flones, with which it ever abounds, are 
fometimes large and fometimes fmall : it varies like- 
wife in its degree of folidity. 
The chief article in the compofition of this feems 
to me to be, that fine burnt material, which is called 
puzzola?ie, whofe binding quality and utility by way of 
cement are mentioned by Vitruvius, and which is to 
be met with only in countries that have been fubjedl to 
fubterraneous fires. It is, I believe, a fort of lime pre- 
pared 
