1849.] LYELL ON THE STRUCTURE OF VOLCANOS. 225 



of the walls, and the fossa grande was perhaps a continuation of this 

 ravine, and was hollowed out by the sea as the mountain was slowly- 

 raised above its level ; but to what extent in this instance an original 

 crater of eruption may have been widened by the sea, I will not ven- 

 ture to speculate. 



Monte Nuovo. 



MM. von Buch and Dufresnoy regard this cone and crater as con- 

 sisting of solid beds of white tuff previously horizontal, which were 

 suddenly upheaved in 1538, so as to dip away in all directions from 

 the centre with the same inclination as the sloping surface of the 

 cone itself. To me it appears, that in addition to all the arguments 

 derived from the absence of rents in the walls and rim of the crater, 

 and the uniformity of structure of the whole funnel-shaped cavity 

 from top to bottom, we have direct historical testimony against such 

 an hypothesis. The cone is 440 English feet high and a mile and a 

 half in circumference, the crater within a few feet as deep as the cone 

 is high. The dip of the beds, from 18° to 20°, is not so great as that 

 which Mr. Darwin observed in the beds of several craters of eruption 

 in the Galapagos Islands, where the tuffs or mud-streams are inclined 

 at angles of from 20° to 30°*. 



We have four descriptions given us by eye-witnesses, of the origin 

 of Monte Nuovo, and there is I think no real discrepancy between 

 them. Two of these narratives, viz. those of Falconi and Pietro di 

 Toledo, are cited by Sir William Hamilton ; another is that of Francesco 

 del Nero, recently published (1846) in the *Neues Jahrbuch,' and 

 translated in the Quarterly Journal of the Geological Society for 1847, 

 while a fourth is that officially drawn up by the physician Porzio 

 at the request of the Viceroy of Naples. 



Francesco del Nero mentions the drying up of the sea near Puzzuoli, 

 and how the soil where the present volcanic orifice exists sank down 

 about forty feet in the morning, and then about midday began to rise 

 up again, so that, where it had subsided four hours before, it was ele- 

 vated into a hill from which fire issued, and where subsequently a great 

 abyss was formed. Such was the violence, the noise and the glare of 

 light, that this eye-witness who was in his garden was much terrified. 

 Many stones and much earth were cast out by the subterranean fire, 

 so that they accumulated round the opening in great quantity. He 

 then describes the shape of the hill, and finishes by referring to Por- 

 zio. Pietro Giacomo di Toledo, after mentioning previous earth- 

 quakes and a slight general rise and drying up of the bed of the sea 

 near the coast, says that at last, on the 29th Sept. 1838, the earth 

 opened near Lake Avernus, and a horrid mouth was seen from which 

 were vomited furiously and with a noise like thunder, fire, stones, 

 and mud composed of ashes. Some of the stones were larger than 

 an ox. The stones went as high as a cross-bow can cany, and then 

 fell down, sometimes on the edge and sometimes into the mouth itself. 

 The mud was of the colour of ashes and at first very liquid, then by 

 degrees less so, and in such quantities that in less than twelve hours 



* Volcanic Islands, p. 107. 



S2 



