ON ITS EXTERIOR. VOLCANOES. 213 



merits of gas, flow from very small basins containing water 

 at the summits of the cones. In these cases the mud is 

 usually cold, but sometimes it has a high temperature, as 

 at Damak in the province of Samarang in Java. The gaseous 

 eruptions, which are accompanied by noise, vary in their 

 nature, consisting sometimes of hydrogen gas mixed with 

 naphtha, sometimes of carbonic acid, and even occasionally 

 of almost pure nitrogen, as Parrot and myself have shewn 

 in the peninsula of Taman, and in the South American 

 volcancitos of Turbaco. ( 21 ) 



After the violent explosions and flames which accom- 

 pany the first appearance of mud volcanoes, and which 

 may not perhaps be common to all in an equal degree, 

 they present to the observer an image of the constant 

 but feeble activity of the interior of the globe. It would 

 seem' as if, soon after their first formation, the channels 

 of communication with the very deep strata having a 

 high temperature became obstructed, and the coldness 

 of the mud emitted appears to indicate that, during the 

 more permanent condition of the phenomenon, the seat of 

 activity is situated not very far below the surface. The 

 reaction of the interior of the earth upon its crust manifests 

 itself far more powerfully in volcanoes properly so called, 

 viz. at points where there exists a communication, either 

 permanent or reopened from time to time, with deep-seated 

 volcanic foci. We must, however, carefully distinguish be* 

 tween volcanic phsenomena of greater or less intensity, 

 between earthquakes, thermal springs, and jets of steam ; 

 mud volcanoes ; the elevation of bell-shaped or dome-shaped 

 trachytic hills or mountains, without openings ; the forma- 

 tion of an opening at the summits of such mountains, or of 



