No. IV. — On the Solfatara of Pozzuoli 12B 



to add materially to our information on its phenomena ; but 

 I should set too high a value on any original observations 

 I have made, or such theoretical considerations as I have 

 casually proposed, if I were not fully aware, that any in- 

 terest which the present series of papers may excite, either 

 in the general or scientific reader, must be almost entirely 

 due to the condensed and epitomized view I have endea- 

 voured to take of the labours of my predecessors on this in- 

 teresting field, who seem for the most part to have taken an 

 insulated survey of some facts, without attempting to embody 

 the results of previous experience, or to furnish the physical 

 inquirer with a statement of such facts as he is naturally de- 

 sirous to be possessed of, without a reference to the bulky 

 and unconnected works from which alone such a body of in- 

 formation can be derived. 



From the nature of the phenomena of the Solfatara, we can 

 best treat the subject by considering, first, its situation and ex- 

 ternal characters, and afterwards its productions, which are ex- 

 tremely varied and important. 



The Solfatara* is the crater of a volcano which can hardly 

 be called entirely extinct. Its connection with the surround- 

 ing hills of Capomazza on the west, Astroni on the north, and 

 the " Colles Leucogaei," extending between Agnano and the 

 sea on the east, is so complete as to disprove the assertion of 

 Ferber, that this crater is an insulated one. The rock of 

 which it is composed is a dark and hard one, which will be 

 more particularly noticed afterwards ; but from the action of 

 the vapours with which this spot abounds, the whole is de- 

 composed at the surface into a white argillaceous matter, 

 which gives the characteristic colour to this tract of country. 

 The crater itself has a nearly oval form, its greatest diameter 

 being in the direction of S. E. to N. W., having a length of 

 2337 French feet ; the smaller one extending from N. E. to 

 S. W. is 1800 feet, and the circumference of the whole 6850. 

 The southern edge is lower than the rest, coinciding, as Breis- 



* This name is sometimes spelled Solfaterra, which perhaps presents the 

 most obvious etymology- Solfatara, however, is much the most usual ex- 

 pression, and may be a corruption, as Eustace supposes, of Su/phuraia, 



