Mr. PouLETT ScROPE on the Volcanic District of Naples. 347 



mould, and were probably projected there by the eruption which produced 

 the hill of Capo-mazza at no very distant period. 



The cone of Astroni is remarkable for its wide and deep crater, surrounded 

 by almost perpendicular banks ; for the occurrence of a small parasitic cone 

 in the middle of the flat plain which forms the floor of this cavity; and for the 

 rock of trachyte, similar to that of Olibano, which shows itself on one part of 

 the basin, cropping out from the conglomerate which composes the chief part 

 of the cone. 



The hills that encircle the Lakes Averno and Agnano have nothing peculiar 

 in their constitution ; consisting, like the last, of beds of loose feldspathose con- 

 glomerate containing large blocks of pumice. The Lago d' Averno was fa- 

 thomed during my residence at Naples by Captain Smith, who had the kind- 

 ness to communicate the result to me. It appears to be from 100 to 102 feet 

 in depth ; beginning to shoal in gradually on all sides, at a distance of about 

 forty feet from the bank. The Lago d'Agnano is a much larger and, I believe, 

 shallower basin : but there is little reason to doubt its resulting equally from 

 volcanic explosions ; though the hifls thrown up around appear to have been 

 much defaced, and their declivities smoothed by meteoric agency, and perhaps 

 also by the addition of ejected matter from other neighbouring vents. There 

 is a strong resemblance between this lake-basin and that of Kloster-laach near 

 Andernach, which is however somewhat larger. The Lago di Ronciglione 

 in the territory of Viterbo is another very similar cavity, and encircled by 

 hills of precisely the same aspect and structure. All are evidently craters pro- 

 duced by the sudden and rapid explosions of a paroxysmal eruption. 



The Monte Barbaro, (the Gaurus inanis of Juvenal,) though one of the 

 largest and highest cones of the Phlegrsean fields, is nevertheless evidently 

 the product of but a single eruption. The crater is extremely deep and large, 

 about a mile in diameter, circular, and perfect, with the exception of two 

 breaches exactly facing one another, on the east and west, — which, however, 

 do not penetrate half-way down to the flat and cultivated plain that occupies 

 the bottom of this remarkable cavity. The rent to the west fronts the Monte 

 Nuovo, and was probably caused by some convulsive shock attendant on the 

 eruption of 1538. Monte Barbaro is composed throughout of indurated tufa, 

 stratified in a direction exactly conformable to its surfaces both internal and 

 external, and therefore dipping away on either side of a supposed vertical and 

 cylindrical band dropped from the ridge of the cone. 



The hill, on the summit of which stands the convent of Camaldoli, to the 

 north of Naples, is still higher than that last described ; measuring 1643 feet 



2 z 2 



