No. III. — Pausilipo and the Lago cCAgnano. 255 



as lenticular, having the greater axes all parallel, and coin- 

 ciding with the direction in which the current, when fluid, (of 

 which he entertains no doubt,) must have progressed. Dr 

 Thompson considered this trachyte (if we may so call it) in- 

 termediate between true lavas and the tufaceous formations ; 

 for it must be distinguished, as Breislak remarks, from the 

 piperino of Rome and Albano, its name being nearly alike ; 

 but these being merely species of tufa exhibiting no marks of 

 fusion like the mass before us. Its situation, too, I consider 

 very interesting, since, as it is overlaid by the ordinary tufa of 

 Pausilipo, it must either have had a prior existence to that 

 substance, and appeared while the waters of the ocean retain- 

 ed their higher relative level, or it must have been subse- 

 quently elevated from below, like our trap rocks, which in 

 some points of view must be considered as the most probable 

 hypothesis, since Mr Scrope has failed in detecting any pecuo 

 liar geognostical position in trachyte, in a neighbouring dis- 

 trict to that we are now considering. * 



Let us now descend from the elevated ridge to the basin in 

 which Lake Agnano is contained at the foot of the steep 

 southern descent of the hill of the Camaldoli ; and we must 

 here introduce a remark or two upon the origin and history 

 of this curious lake. After consulting all the authorities of 

 which I am possessed on this subject, and attentively con- 

 sidering the state of the localities as I myself observed them, 

 I feel unable to come to any decisive opinion on the sub- 

 ject. Certain it is that this lake is never mentioned by clas- 

 sic authors, and is first noticed by some writers of the middle 

 ages, under the name of Lacus Anclanus, supposed to have 

 been so called from a town named Angulanum, which is 

 thought to have stood on its banks, and which some still 

 absurdly maintain is to be seen in ruins under water, -[- a 

 fable not uncommon in its nature, and which, I believe, is en- 

 tirely refuted. The question which remains to be solved is, 

 why this lake, if it existed in the time of the Romans, is ne- 

 ver mentioned by their authors, in a region, the other features 



" Geological Transadions, — uhi. sup. 



"I" Ferrari, Guida di Napoli, and Breislak, ii. 48. 



