Note 29 — LETTER V.
Reading edition
These are his words, book II. chap. vi.
"De Pulvere Puteolano.
"Est etiam genus pulveris, quod efficit naturaliter res admirandas. Nascitur in regionibus Baïanis, et in agris municipiorum, quæ sunt circa Vesuvium montem, quod commixtum cum calce et cæmento non modo cæteris ædificiis præstat firmitates, sed etiam moles, quæ construuntur in mari, sub aqua solidescunt. Hoc autem fieri hac ratione videtur, quod sub his montibus et terra ferventes sunt fontes crebri, qui non essent, si non in imo haberent, aut de sulfure, aut alumine, aut bitumine ardentes maximos ignes: igitur penitus ignis, et flammæ vapor per intervenia permanans et ardens, efficet levem eam terram, et ibi, qui nascitur tophus, exugens est, et sine liquore. Ergo cum tres res consimili ratione, ignis vehementia formatæ in unam pervenerint mixtionem, repente recepto liquore una cohærescunt, et celeriter humore duratæ solidantur, neque eas fluctus, neque vis aquæ potest dissolvere."
About Baïa, Puzzole, and Naples, we have an opportunity of remarking the truth of these last words. Several of the piers of the ancient harbour of Puzzole, vulgarly called Caligula's bridge, and which are composed of bricks joined with this sort of cement, are still standing in the sea, though much exposed to the waves; and upon every part of the shore you find large masses of brick-walls rounded and polished by friction in the sea, the brick and mortar making one body, and appearing like a variegated stone. Large pieces of old walls are likewise often cut out into square pieces, and made use of in modern buildings instead of stone.
Soon after the first quotation, Pliny says, "Si ergo in his locis aquarum ferventes inveniuntur fontes, et in montibus excavatis calidi vapores, ipsaque loca ab antiquis memorantur pervagantes in agris habuisse ardores, videtur esse certum ab ignis vehementia ex topho terraque, quemadmodum in fornacibus et a calce, ita ex his ereptum esse liquorem. Igitur dissimilibus, et disparibus rebus correptis, et in unam potestatem collatis, callida humoris jejunitas aqua repente satiata, communibus corporibus latenti calore confervescit et vehementer effecit ea coire, celeriterque una soliditatis percipere virtutem."