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



otherwise explained); and for this reason I should prefer the conclusion, — that 

 the rise of the plains of Campania from below the sea was produced by some 

 convulsive crisis of subterraneous expansion, occasioned perhaps by the long 

 obstruction of the superficial vents, — those natural safety-valves that by their 

 occasional activity at present, may be supposed to obvia-e the recurrence of 

 such tremendous operations. 



The south-eastern side of the bay of Naples likewise contains some scat- 

 tered volcanic formations. They show themselves in the recesses of the lime- 

 stone mountains, both at Vico and Sorrento. No crater or regular cone is 

 discoverable ; but unequal deposits of tufa enveloping massive beds of tra- 

 chytic lava, of an ash-gray colour, extremely light, porous, earthy, and brittle, 

 show themselves on many points ; particularly around Sorrento, where they 

 form a plain backed by a crested range of limestone, and appearing to have 

 been levelled by the action of the sea, though it is now raised more than two 

 hundred feet above the actual shore, — an additional fact in favour of the 

 recent elevation of this line of coast. 



At the Punto di Campanella, the extremity of this promontory (which is 

 itself composed of a sandstone, probably the new red, cropping out from below 

 the great formation of Apennine limestone near Massa), another deposit of 

 tufa is met with, which contains masses of obsidian coloured with various 

 shades of blue, and frequently showing the small globular concretionary 

 structure (pearlstone). The globules are concentric, but not radiated. 



