ROCKS. 247 



opment of large quantities of pure aqueous vapor ; subsequent- 

 ly, when the volcano becomes a solfatara, by aqueous vapors 

 mixed with sulphureted hydrogen and carbonic acid gases ; 

 and, finally, when it is completely cooled, by exhalations of 

 carbonic acid alone. There is a remarkable class of igneous 

 mountains which do not eject lava, but merely devastating 

 streams of hot water,* impregnated with burning sulphur and 

 rocks reduced to a state of dust (as, for instance, the Galun- 

 gung in Java) ; but whether these mountains present a normal 

 condition, or only a certain transitory modification of the vol- 

 canic process, must remain undecided until they are visited by 

 geologists possessed of a knowledge of chemistry in its present 

 condition. 



I have endeavored in the above remarks to furnish a gen- 

 eral description of volcanoes — comprising one of the most im- 

 portant sections of the history of terrestrial activity — and I 

 have based my statements partly on my own observations, but 

 more in their general bearin,^ on the results yielded by the la- 

 bors of my old friend, Leopold von Buch, the greatest geogno- 

 sist of our own age, and the first who recognized the intimate 

 connection of volcanic phenomena, and their mutual depend- 

 ence upon one another, considered with reference to their rela- 

 tions in space. 



Volcanic action, or the reaction of the interior of a planet on 

 its external crust and surface, was long regarded only as an 

 isolated phenomenon, and was considered solely with respect 

 to the disturbing action of the subterranean force ; and it is 

 only in recent times that — greatly to the advantage of geog- 

 nostical views based on physical analogies — volcanic forces 

 have been regarded as forming 7iew rocks, and iranforining 

 those that already existed. We here arrive at the point to 

 which I have already alluded, at which a well-grounded study 

 of the activity of volcanoes, whether igneous or merely such 

 as emit gaseous exhalations, leads us, on the one hand, to the 

 mineralogical branch of geognosy (the science of the texture 

 and the succession of terrestrial strata), and, on the other, to 

 the science of geographical forms and outlines — the configura- 

 tion of continents and insular groups elevated above the level 



* Compare Reiuwardt and Hoflfmauu, iu Poggendorf 's Annalen, bd. 

 xii., s. 607 ; Leop. von Buch, Descr. des lies Canaries, p. 424-426. Tiie 

 eruptions of argillaceous mud at Carguairazo, when that volcano was 

 destroyed iu 1698, the Lodazales of Igualata, and the Moya of Pelileo 

 —all on the table-land of Quit^ — arc volcanic phenomena of a similar 

 nature. 



