6 Account of the 



celebrated by Horace (Ode 4, lib. iii,), is a volcanic mountain 

 rising in the midst of the chain of the Apennines, and the neigh- 

 bouring town of Acherontia, " which Horace calls Nidus AcJie- 

 roJitia, probably derived its name from being situated in an 

 elevated and circular cavity on a mountain, such as the crater 

 of an extinct volcano would exhibit, borrowing its name from 

 the Lacus Acherontiae, now Fusaro, near Naples.'** — Daubeny, 

 141. The Lacus Amsanctus appears also to be the crater of a 

 volcano. — Id. 142. 



Volcanic action has long ceased in every part of this district, 

 except at its southern extremity, and there are no distinct human 

 records of that action, except in Vesuvius and the country imme- 

 diately contiguous to it. But the proofs of the agency of fire 

 in distant ages, throughout the tract I have named, are written 

 in characters which cannot be mistaken. The whole face of this 

 tract is not, however, occupied by volcanic products : these are 

 interrupted in various places by the Apennine limestone and 

 the tertiary deposits rising up in the midst of them. An exact 

 representation of the mineral structure of the district, could only 

 be given by means of colours upon a map on a large scale. 



The volcanic products are of various kinds. They consist of 

 hard lava of a close, compact, semi-crystalline structure, resem- 

 bling rocks of common occurrence in various parts of the United 

 Kingdom, known by the names of greenstone, basalt, whinstone, 

 &c. ; also of a stone nearly as hard as the preceding, but less 

 compact, and evidently composed of an agglutination of frag- 

 ments. This is known by the name of volcanic tiiff' or tij/ci- 

 Tufa differs from lava in this, that it has never run in a fluid 

 state, but is an aggregate of scoriae, lapilli, sand and ashes ; sub- 

 stances, all of which have been subjected to fire, but thrown out 

 by the volcano and deposited far from the craters from whence 

 they were ejected. It is, besides, very common for volcanoes to 

 throw out a vast quantity of water, which, mixing with the 

 scoriae and ashes, forms vast streams of liquid mud of greater 

 or less density, as the ashes bear a greater or less proportion to 

 the water. When the water evaporates, the mass becomes com-, 

 pact and hard, and thus tufa is formed. Such was the stream 

 of volcanic matter which covered Herculaneum ; ashes agglu- 

 tinated by the mixture of water and converted into a hard ston^. 



