The composition of Roman mortar and cement is described under STRUCTURA: we here notice the different kinds
of sand employed,--a subject to which Vitruvius has devoted a chapter
(2.4). He reckons four kinds of pit sand (fossilis
), besides sea and river sand; the black (nigra
), the white (cana
), the red (rubra
), and the
cf. Varr. L.
1.9, 2). Pliny recognises only the distinctions of sea,
river, and pit sand, not those of colours (H. N.
§ § 54, 55). In another chapter (2.6) Vitruvius
describes the pulvis Puteolanus,
volcanic sand of the [p. 1.179]
Vesuvius, as a different material, unaware that it is substantially
identical with that of the Roman Campagna. The modern name pozzolana
is applied indifferently to both.