VOLCANOES. 24A 



Himalaya, it is not the latter chain, which is nearest to the 

 ocean, but the two inner ranges, the Thianschan and the 

 Kuen-lun, at the distance of 1600 and 720 miles from the sea, 

 which have fire-emitting mountains like Etna and Vesuvius, 

 and generate ammonia, like the volcano of Guatimala. Chinese 

 writers undoubtedly speak of lava streams when they describe 

 the emissions of smoke and flame, which issuing from Po 

 schan devastated a space measuring ten li,* in the first and 

 seventh centuries of our era. Burning masses of stone flowed, 

 according to their description, " like thin melted fat." The 

 facts that have been enumerated, and to which sufficient 

 attention has not been bestowed, render it probable that the 

 vicinity of the sea, and the penetration of sea-water to the 

 foci of volcanoes, are not absolutely necessary to the erup- 

 tion of subterranean fire, and that littoral situations only 

 favour the eruption by forming the margin of a deep sea 

 basin, which, covered by strata of water, and lying many 

 thousand feet lower than the interior continent, can offer but 

 an inconsiderable degree of resistance. 



The present active volcanoes, which communicate by per- 

 manent craters simultaneously with the interior of the earth 

 and with the atmosphere, must have been formed at a subse- 

 quent period, when the upper chalk strata, and all the tertiary 

 formations, were already present ; this is shown to be the fact 

 by the trachytic and basaltic eruptions which frequently form 

 the walls of the crater of elevation. Melaphyres extend to 

 the middle tertiary formations, but are found already in the 

 Jura limestone, where they break through the variegated sand- 

 stone, f We must not confound the earlier outpourings of 

 granite, quartzose porphyry and euphotide, from temporary 

 fissures in the old transition rocks, with the present active 

 volcanic craters. 



The extinction of volcanic activity is either only partial HI 

 which case the subterranean fire seeks another passage of 

 escape in the same mountain chain or it is total, as in 

 Auvergne. More recent examples are recorded in historical 



* [A li is a Chinese measurement, equal to about 1-3 Oth of a mile> 

 -7Y. 



+ Dufrenoy et Elie de Beaumont, Explication de la 

 dt *a France, t. i. p. 89, 



