350 Mr. PouLETT Scrope on the Volcanic District of Naples. 



been much degraded, owing to its exposure to a heavy sea-swell both from the 

 north-west and south. It appears composed throughout of a frame-work of 

 indurated tufa covered with strata of the same substance in an incoherent 

 state. One bed of trachytic lava enveloped in the tufa, is visible in the cliffs 

 on the north-western side of the island *. 



The promontory of Misenum has been once a very perfect cone with a 

 regular crater, but the action of the waves has worn it away nearly to the 

 centre, by which a fine natural section is afforded of the mass of indurated 

 tufa of which it consists. The mantle-form disposition of the strata dipping 

 away from the circular ridge, already noticed as characteristic of a volcanic 

 cone, is no where better exemplified f. 



The island of Nisida also is a small but very regular cone, with a crater 

 into which the sea has at length effected its entrance, by a breach on the 

 western and exposed side. The bluff cliffs disclosed by this continual degra- 

 dation show the same internal structure as those of Misenum |. 



Close upon Nisida rises the promontory of Pausilipo, a long and narrow 

 ridge, connected with three or four similar hills called the Vomero, Capo di 

 Chino, and Capo di Monte, which rise immediately behind Naples, and on 

 a part indeed of which that town is built. All are composed chiefly of sohd 

 tufa, stratified mantle-wise ; but though they partly embrace three or four de- 

 cidedly crateriform basins, they have little of the regularity of ordinary cones. 

 In the solid tufa quarried out of these hills I have found shells of the genera 

 ostrea, cardium, buccinum, and patella, differing in nothing from the species 

 that at present inhabit the bay of Naples : also pieces of unmineralized 

 wood, retaining great flexibility of fibre, and burning with a slow flame and a 

 resinous smell. The loose conglomerate of Capo di Chino envelops burnt and 

 half-fused fragments of indurated tufa passing into porphyritic pitchstone, 

 masses of this last substance with a minute globular concretionary structure 

 (pearlstone), and others passing into complete obsidian ; besides pumice, and 

 a great variety of feldspathose lavas in fragments. At Capo di Monte vertical 

 veins are observed to penetrate the hard tufa-rock. They are from six inches 

 to two feet in width, and consist equally of tufa, but of a very fine grain, ex- 

 tremely hard, with a conchoidal fracture, and seamed with parallel stripes of 

 a coarser grain. The appearance of theso veins suggests the idea of their 

 having resulted from fissures formed in the tufa before it was entirely conso- 

 lidated, and filled by a deposit of its finest particles, from the water that 

 exuded into the cleft from either side. Indeed the hard tufa, of which, as is 



* See Plate XXXIV. fig. 6. + Ibid. % See Plate XXXIV. fig. 4. 



