1859.] SCEOPE CONES AND CRATERS. 537 



scoriae and fragmentary matter several thousand feet high, lasted for 

 a period of twenty days, and were found at the end of that time to 

 have drilled through the previous solid core of the mountain an 

 abrupt circular chasm or caldron three miles in circumference and 

 more than 1000 (some observers estimated it at 2000) feet in depth. 

 The mass of matter removed from this cavity, together with a 

 large portion of the former external summit of the cone (which was 

 found to have lost above 600 feet in height after the eruption), had 

 been blown into the air. The eructations consisted of continued 

 discharges of aqueous vapour — in fact, of steam, which rose to a still 

 greater height than the fountain of solid matters (at least 10,000 

 feet), in a pillar composed to appearance of distinct globular volumes 

 or puffs of steam, which, driven upwards with immense force, rolled 

 over and over one another, looking like so many great balls of cotton, 

 and spread laterally in some degree, as the resistance of the atmo- 

 sphere checked the velocity of their ascent, while fresh discharges 

 pressed upon them, rushing up from the vent beneath. Each puff 

 or globe of vapour evidently consisted of the contents of a great 

 bubble which had risen up through the molten lava in the chinrne}'- 

 of the volcano and burst on reaching its surface. It was exactly as 

 if a continuous succession of discharges took place from some colossal 

 Perkins's steam-mortar in the axis of the mountain. And to the 

 equal pressure in all directions of the enormous expansive force of 

 these flashes of steam was owing, of coui'se, the circular section of 

 the crater, or canal of discharge, gradually bored by this giant artil- 

 lery through the heart of the cone, — continuous discharges taking 

 place from greater and greater depths, as the surface of the ebullient 

 lava fell within the vent. By degrees, however, the explosions di- 

 minished in force and frequency, until at length the tension of the 

 vapour-bubbles bursting at the bottom of the crater seemed no 

 longer to have power to throw off beyond its encircling rim the 

 fragments which fell within it, and the accumulation of which at 

 length wholly stifled the explosions, and the eruption terminated. 

 That is what I witnessed in 1822 ; and it is thus, I believe, that 

 volcanic craters of large size are always formed — not by any single 

 mine-like explosion, such as the upheavalists have imagined. 



The mass of fragmentary' matter thrown up during the eruption 

 was for the most part triturated, by repeated ejection, into fine ashes, 

 which were carried by the wind to great distances, or washed down 

 the sides of the mountain in streams of mud by the torrents of 

 rain that followed the eruption. On the flanks of the cone itself, 

 the coarser scoriae and fragments accumulated of course in great 

 abundance. Several of the ejected masses which fell towards 

 Ottaiano on the eastern slope measured 25 feet or more in circum- 

 ference, and weighed several tons; but the average depth of the 

 fragmentary matter spread by this eruption over the entire area 

 of the mountain, or "within a radius of some five miles, did not exceed 

 a foot or two. At Naples, distant fifteen miles, the ashes fell to a 

 depth of only about half an inch, although the wind drove them in that 

 direction ; and from this observation I was led to reflect on the far 



