232 REACTION OP THE INTERIOR OP THE EARTH 



lance the hydrostatic pressure of the waters of the sea, and 

 to allow them, under certain conditions, free access to the 

 foci. ( 235 ) We must learn whether the presence of the metallic 

 chlorides, or even of marine salt in the fissures and crevices in 

 the sides of craters, and the frequent admixture of hydro- 

 chloric acid in the aqueous vapours, necessarily imply such 

 access of the sea water. Finally, we must inquire if the in- 

 activity of volcanoes (whether temporary, or final and com- 

 plete,) is dependent on the interruption of the channels by 

 which either the sea or fresh water previously penetrated ; 

 or if the absence of flames and of hydrogen gas (not of sul- 

 phuretted hydrogen which belongs rather to solfataras than 

 to active volcanoes,) is directly opposed to the hypothesis 

 which attributes their activity to the decomposition of great 

 masses of water. The discussion of these important physi- 

 cal questions does not belong to a work like the present : 

 but whilst on the subject of the geographical distribution of 

 volcanoes, it is proper to notice that all active volcanoes 

 are not in close proximity to the sea ; since on the new 

 continent, Jorullo, Popocatepetl, and the Volcano de la 

 Fragua, are respectively 80, 132, and 156 geographical miles 

 from the ocean ; and even in central Asia, a fact to which 

 Abel Remusat ( 236 ) first called the attention of geologists, 

 we find a great volcanic chain, the Thian-schan (celestial 

 mountains,) to which belong the Pe-schan from whence 

 lava issues, the solfatara of Urum-tsi, and the still ac- 

 tive " fire mountain" (Ho-tscheu,) of Turfan, almost equi- 

 distant from the shores of the Polar Sea and of the Indian 

 Ocean (1400 and 1528 miles.) Pe-schan is also fully 

 1360 miles from the Caspian Sea, and 172 and 208 miles 

 respectively from the great lakes of Issikoul andBalkasch. ( 237 ) 

 It is deserving of notice that, of the four great parallel 



