236 Baron Humboldt on the Structure and Actum of 



on their huts ashes which the earth had vomited by opening up 

 on all sides. On the contrary, in the periodical and ordinary 

 explosions of volcanoes, the ashes terminate each partial erup- 

 tion. Besides, the younger Pliny's letter contains a passage, 

 which clearly shews, that, from the commencement, without the 

 influence of any cause that could have heaped them up, the dry 

 ashes that fell directly from above, had attained a height of four 

 or five feet. " The court,*" says he in the course of his narra^ 

 tive, which had to be passed in order to enter the chamber 

 in which Pliny reposed, " was 6o filled with ashes and pumice, 

 that, if he had delayed his coming out any longer, he would 

 have found the entrance shut up."" In an inclosed space, like 

 that of a court, the action of the wind, by which the ashes are 

 collected, could not by any means have been very considerable. 



I have ventured to interrupt my comparative examination of 

 volcanoes by particular observations made on Vesuvius, both on 

 account of the great interest which the last eruption has excit- 

 ed, and on account of the remembrance of the catastrophe of 

 Pompeii and Herculaneum, which every considerable fall of 

 ashes involuntarily brings to the mind. I have brought toge- 

 ther, in a supplement, all the elements of the barometrical mea- 

 surements and notices respecting geological collections that I 

 have had an opportunity of making, towards the end of 1822, at 

 Vesuvius and in the Phlegrean fields, near Pouzzuolo. This small 

 collection, together with the rocks which I brought from the 

 Euganean mountains, and those which M. von Buch collected on 

 a journey to the valley of Flemme, between Cavalere and Pre- 

 dazzo, in the southern Tyrol, are deposited in the Royal Mu- 

 seum of Berlin, an establishment which, by its utility, perfectly 

 corresponds to the noble intentions of the monarch, and of which, 

 the geognostical department, containing specimens from the most 

 remote regions, is, in this respect, superior to any collection of 

 this kind in existence. 



We have been considering the form and action of those vol- 

 canoes which keep up a regular communication with the interior 

 of the earth, by means of craters. Their summits are masses of 

 trachyte and lava, raised up by elastic powers, and traversed by 

 veins. The permanence of their action gives rise to the conclu- 

 sion, that their structure is very complicated. They have, so 



