Volcanos. 109 



and of which the enumeration here would he too long for our 

 analysis. 



" In the third class, or under the phase of prolonged intermit- 

 tences, the number is even greater than in the preceding ; and as 

 novelty, in the case of eruptions of this nature, is added to the 

 naturally terrific circumstances attending them, these are the 

 eruptions which have excited the greatest attention, and which 

 make the greatest figure in history. The author proceeds to 

 sketch the general appearances attending an eruption of this 

 nature. 



" They are commonly preceded by earthquakes of different de- 

 grees of intensity and duration, and with loud sounds or detonations 

 resembling the noise of ordnance and musketry, apparently pro- 

 duced by the disengagement of aeriform fluids, and the increase 

 of bulk in the fluid rocks ; and their sounds are conveyed through 

 the solid earth, not by means of the air. The atmosphere at this 

 time is remarked to be in a peculiar state of stillness, attended by 

 a sense of oppression. 



" During this period also, springs are apt to disappear, so that 

 wells become dry ; and it is known that the extent of this affec- 

 tion is sometimes very considerable. 



" When the eruption first appears, it is generally with sudden 

 and* great violence. Explosions, apparently from confined air, 

 take place with loud noises, and succeeding each other with 

 rapidity, and often with increasing force ; the vent being, com- 

 monly, the central point or crater of the mountain. And in its 

 attempt to escape, this air throws up fragments of rock, which 

 sometimes fall back into the crater, and are again repeatedly 

 projected, together with clouds of aqueous vapor. And as the 

 fragments also are often broken into small pieces, and even into 

 dust, this, uniting to the vapor or mixing with it, produces dense 

 black clouds, or smoke, often assuming the form of a column of 

 entangled or successively formed clouds. 



" Having arrived at a certain height, this column generally 

 spreads laterally or horizontally, forming, if the air is calm, a 

 shape resembling that of a pine-tree, of if there be wind, a hori- 

 zontal stream. Out of this cloud proceed lightnings of great 

 vividness, while the falling of the dust, added to the density of 

 the cloud, produces darkness over the surrounding country. 

 The melted rock or lava now boils up in the crater, and is 

 often so thrown up into jets by the extricated air, as to resem- 

 ble flames ; and at length it either boils over the edge of the 

 crater, so as to run down the mountain, or else finds an issue 

 laterally, by some crevice, equally flowing down in a stream, 

 which holds its course as circumstances permit, down to the lower 

 grounds. 



