320 D. Forbes — On Vokanos, 



poured out from the very base of tlie cones, forming a fiery river ap- 

 parently about three miles across, which destroyed all before it, 

 cutting through a large pine forest, and at one place leaping like a 

 cascade of liquid fire over a precipice some 150 feet in height. 



The formation of a new, or re-opening of an old volcanic vent, is 

 nsually accompanied by a terrific explosion, often to be heard at 

 immense distances ; thus in 1812, the outburst of the volcano of San 

 Vincent was heard in the north of South America, some 700 miles 

 distant. The enormous force developed by the rush of gases and 

 vapours from the fissure may be imagined, when it is known that in 

 the eruption of Mount Ararat, in 1840, huge masses of rocks, weighing 

 as much as 25 tons, were thrown out of the crater. Cotopaxi is said 

 to have even hurled a 200-ton rock to a distance of nine miles, while 

 the volcano of Antuco, in Chili, in 1828, sent stones flying to a dis- 

 tance of 36 miles from its orifice. 



The issue of gaseous matter from the crater of a volcano is often 

 described as a column of flame — this is incorrect ; for although pos- 

 sibly a little burning hydrogen, or sulphuretted hydrogen might be 

 present, especially on the outer edge of the column, the appearance 

 of the column or fountain of flame is in reality due to the gaseous 

 matter of which it consists being illuminated by the fragments of red- 

 hot rock and molten lava thrown up along with it (like sparks in 

 fireworks), assisted by the reflection from the red-hot sides of the 

 crater itself, and from the surface of the molten lava below. 



The chemical composition of the gasiform emanations from voloanos 

 proves that they are in greater part incombustible, and therefore 

 does not support the idea that the body of such a column of vapour 

 and gases could be in flames, i.e., actually burning. On the outside 

 of the column, however, innumerable brilliant scintillations of a 

 bluish colour are frequently seen, due to particles of sulphur taking 

 fire as they come in contact with the outer air, and patches of melted 

 sulphur are splashed about, burning brightly as they fall through the 

 air on to the slopes of the cone. The emission, or belching forth, as 

 it has been called, of the gaseous matter, with its accompanying red- 

 hot ashes and scorise, is more an intermittent than a continuous 

 operation. When an eruption is at its height, the spasmodic puffs or 

 blasts are jerked out at intervals of but a few seconds, attended by a 

 terrific roaring or bellowing noise difficult to describe in words. 



The buried cities of Stabi^, Herculaneum, and Pompeii, covered 

 up in parts to the depth of 100 feet with the ashes of Vesuvius, are 

 ocular proofs of the vast quantity which can be sent out of a volcanic 

 vent during an eruption. The volcano of Sangay in Ecuador, in 

 constant activity since 1728, has buried the country around it to a 

 depth of 4000 feet under its ashes, and a French geologist has esti- 

 mated that in the course of only two days the volcano of Bourbon 

 has thrown out no less than 300,000 tons of volcanic ashes. The 

 immense distances to which these ashes may be transported by the 

 winds is no less surprising ; the ashes of Vesuvius in the eruption 

 which buried Pompeii darkened the sun at Eome, and were carried 

 as far as Syria and Egypt. Those from San Vincent in 1812 are 



