164 KEACTION OF THE INTERIOR OF THE EARTH 



cending to the height of many thousand feet, and that 

 the same internal force is at work as that which gives 

 rise to colossal craters of elevation, and even to the 

 mighty devastating, lava-pouring volcanoes of Etna and 

 the Peak of Teneriffe, and to those of Cotopaxi and 

 Tunguragua from which scoriae are ejected. 



Among the manifold and cumulative phenomena of 

 the reaction of the interior against the external crust, 

 I will first consider separately those whose essential 

 character is simply dynamical, and which consist of un- 

 dulations of the solid strata, being a volcanic activity 

 not necessarily accompanied by chemical alteration of 

 substances, or by the eruption or production of any fresh 

 substance. In the other phenomena of the reaction of 

 the interior against the exterior, in gas- and mud- 

 volcanoes, in burning naphthas and salses, and in the 

 great burning mountains which were first, and for a 

 long time exclusively, termed volcanoes, there are 

 always present, the production of some fresh sub- 

 stance (gaseous or solid), processes of decomposition 

 and evolution of gases, and the formation of rock from 

 particles arranged in crystalline order. These are, 

 speaking in the most general terms, the distinctive 

 marks or signs of the volcanic vital activity of our 

 planet. In so far as this activity is to be principally 

 ascribed to the high temperature of the interior of the 

 earth, it is probable that all heavenly bodies which have 

 been condensed from a gaseous to a solid state, with an 

 accompanying enormous extrication of heat, must 

 present analogous phsenomena. The little that we 

 know of the configuration of the Moon's surface seems 

 to afford indications ( 2 - 7 ) in correspondence with this 



