Specimens of tufa, c 1770.
© Science Museum / Science & Society Picture Library
Hand-coloured etching by Peter Fabris (active 1768-1779). Illustrated plate from William Hamilton's study of Italian volcanoes, 'Campi Phlegraei' (published in Naples, 1776). Specimens of tufa removed from quarries near the Grotto of Pausilipo (now known as Posillipo), southern Italy, showing (1) tufa with oyster shells, (2) with a piece of lava, (3) with volcanic cinder and (4) with green tufa. Tufa is a mixture of ashes and pumice stones thrown up by volcanoes in liquid mud form. Hamilton's book is a seminal work on the nature and effects of volcanic explosions.