VOLCANOES. 233 



others, they only proceed from the crater, or at any rate from 

 very considerable heights. These important and involved 

 relations can only be explained by very accurate crystallo- 

 graphic and chemical investigations. My fellow-traveller in 

 Siberia, Gustav Rose, and subsequently Hermann Abich, 

 have already been able, by their fortunate and ingenious 

 researches, to throw much light on the structural relations of 

 the various kinds of volcanic rocks. 



The greater part of the ascending vapour is mere steam. 

 When condensed this forms springs, as in Pantellaria,* where 

 they are used by the goatherds of the island. On the morning 

 of the 26th of October, 1822, a current was seen to flow 

 from a lateral fissure of the crater of Vesuvius, and was long 

 supposed to have been boiling water ; it was, however, shown 

 by Monticelli's accurate investigations to consist of dry ashes 

 which fell like sand, and of lava pulverised by friction. The 

 ashes which sometimes darken the air for hours and days 

 together, and produce great injury to the vineyards and olive 

 groves, by adhering to the leaves, indicate by their columnar 

 ascent, impelled by vapours, the termination of every great 

 earthquake. This is the magnificent phenomenon which Pliny 

 the younger, in his celebrated letter to Cornelius Tacitus, 

 compares, in the case of Vesuvius, to the form of a lofty 

 and thickly-branched and foliaceous pine. That which is 

 described as flames in the eruption of scoria?, and the radiance 

 of the glowing red clouds that hover over the crater, cannot 

 be ascribed to the effect of hydrogen gas in a state of com- 

 bustion. They are rather reflections of light which issue 

 from molten masses, projected high in the air, and also re- 

 flections from the burning depths, whence the glowing vapours 

 ascend. We will not, however, attempt to decide the nature 

 of the flames which are occasionally seen now, as in the time 

 of Strabo, to rise from the deep sea during the activity of 

 littoral volcanoes, or shortly before the elevation of a volcanic 

 island. 



WTien the questions are asked, what is it that burns in the 

 volcano ? what excites the heat, fuses together earths and 

 metals, and imparts to lava-currents of thick layers a degree 



* [Steam issues from many parts of this insular mountain, and several 

 hot springs gush forth from it, which form together a lake 6000 feet in. 

 circumference. Daubeney, op. cit.] Ti\ 



