132 M, Hvmholdt on Volcanoes, [Aug. 



and without the effect of accumulation by water. " The court 

 which led to his [uncle^s] apartment," he says, " being now 

 almost filled with ashes and pumice, it would have been impos- 

 sible for him, if he had continued there any longer, to have made 

 his way out." In the narrow space of a court, the wind could 

 not have had any great effect in accumulating the ashes. 



I have ventured to interrupt my comparative view of volca- 

 noes by observations solely on Vesuvius, partly on account of 

 the great interest which the last eruption has excited, and partly 

 because every great fall of ashes almost involuntarily reminds us 

 of the classic ground of Pompeii and Herculaneum.* We have 

 hitherto considered the form and the effects of those volcanoes 

 which are in permanent communication with the interior of the 

 earth, by means of a crater. Their summits are raised masses 

 of trachyte and lava, intersected by numerous veins ; the dura- 

 tion of their effects causes us to believe that they have a very 

 stable and undisturbed structure. They possess, I may say, a 

 more individual character, which remains the same during long 

 periods. Neighbouring mountains often furnish completely 

 different products, leucite-lava, and felspar-lava ; obsidian, with 

 pumice, and basaltic masses containing ohvine. They belong 

 to the newer phsenomena of the earth, pass generally through all 

 the strata of secondary rocks, and their eruptions and currents 

 of lava are of later origin than our valleys. Their hfe, if I may 

 use that expression, depends upon the manner and duration of 

 their connexion with the interior of the earth. They often rest 

 for centuries, suddenly take fire again, and terminate as solfa- 

 taras, which emit steam, gases, and acids. Sometimes, as on 

 the Peak of Teneriffe, their summit has already become such a 

 depository of reproduced sulphur, while mighty currents of lava 

 flow from the sides of the mountain, hke basalt below, and 

 above, where the pressure is less, like obsidian with pumice. 



Independently of these with permanent craters, volcanic 

 phsenomena of another kind exist, which have been observed 

 less frequently, but are principally interesting in geognosy, and 

 remind us of the primitive world ; that is to say, of the earhest 

 revolutions of our earth. Mountains of trachyte suddenly 

 open, eject lava and ashes, and close again, perhaps, for 

 ever : thus was it with the mighty Antisana ; and thus with the 

 Epomaeus, in Ischia, in 1302. Such an eruption sometimes 

 talces place even in the plain, as in the high lands of Quito ; in 

 Iceland, far from Hecla ; and in Eubcea, in the Lelantic fields. 

 Many of the islands which have been raised up are owing to these 

 temporary phenomena. In these cases the communication with 

 the interior of the earth is not permanent, and the effect ceases 

 as soon as the fissure, which is the communicating channel, is 



• The author here mentions a paper on the data of his measurements at Vesuvius, 

 which was unsuitaWe for reading ; and then proceeds to notice a collection of minerals 

 that f^ brought with liim, and which will be added to the Royal Aluseum at Berlin. 



