Lava is much used for paving-stones in the neighborhood of volcanic districts, where pozzolana (for cement) and pumice stone are also important.
The mineral wealth of the Cyclades has hitherto been much neglected; iron ore is exported from Seriphos, manganese and sulphur from Melos, and volcanic cement (pozzolana) from Santorin.
Six centuries elapsed before the accidental discovery of a sepulchral chamber by some labourers digging for pozzolana earth (May 31, 1578) revealed to the amazed inhabitants of Rome " the existence," to quote a contemporary record, " of other cities concealed beneath their own suburbs."
According to modern physicians it is impossible to live many days in the caves of pozzolana in which many of the catacombs are excavated."
1 The pozzolana is the material required for building purposes, for admixture with mortar; and the sandpits are naturally excavated in the stratum which supplies it.
It exported iron from Elba, mosaics, pottery, manufactured locally with earth from Ischia (which was in considerable demand until 1883), sulphur (which indeed was extracted in the neighbourhood until the 18th century), probably alum (which is still worked), perfumes, pozzolana earth (taking its name from the place), cretaceous earth for mixing with grain (alica) from the Leucogaean hills, glass cups engraved with views of Puteoli, mineral dyes (the blue invented.
C. i is on the earliest dwellings of man; C. 2 on systems of Thales, Heraclitus, Democritus, &c.; c. 3 on bricks; c. 4 on sand; c. 5 on lime; c. 6 on pozzolana; c. 7 on kinds of stone for building; c. 8 on methods of constructing walls in stone, brick, concrete and marble, and on the materials for stucco; c. 9 on timber, time for felling it, seasoning, &c.; and c. to on the fir trees of the Apennines.
The matter transported consisted of soil of various kinds - sand, ashes, fragments of lava, pozzolana and whitish pumice, enclosing grains of uncalcined lime, similar in every respect to those of Pompeii.
In the part of Herculaneum already excavated the corridors in the upper portions of the theatre are compactly filled, up to the head of the arches, with pozzolana and pumice transformed into tufa (which proves that the formation of this stone may take place in a comparatively short time).
Its mineral baths are frequented in summer; and the volcanic pozzolana earth (also found near Rome), used now as in Roman times for making cement and concrete, derives its name from the place.
In the older districts there is a countless variety of narrow gloomy streets, many of them steep. The houses are mostly five or six storeys high, are covered with stucco made of a kind of pozzolana which hardens by exposure, and have large balconies and flat roofs.