162 KEACTION OF THE INTERIOR OF THE EARTH 



II. 



Reaction of the interior of the earth on its exterior, showing itself, 



(a) dynamically, by waves of agitation, or " earthquakes ; " 



(Z>) by the increased temperature of the water of springs, 

 and the admixture of other substances, as salts and gases, in 

 mineral and thermal springs ; (c) by the breaking forth of 

 elastic fluids, accompanied at times by phenomena of spon- 

 taneous ignition (gas- and mud-volcanoes, burning naphtha, 

 and salses) ; (d) by the grand and powerful action of 

 volcanoes proper, in which, (by permanent channels of com- 

 munication with the atmosphere through fissures and craters), 

 earths molten at profound terrestrial depths are erupted as 

 glowing scoriae, partly subjected, at the same time, to pro- 

 cesses whereby they are changed into crystalline rocks, and 

 partly poured forth in long narrow streams of lava. 



IN order to maintain, in accordance with the fundamental 

 plan of my work, the connecting links uniting all telluric 

 phenomena, and to preserve the representation of the 

 concurrent action of forces in a single system, we must 

 here recall how, beginning from the general properties 

 of matter, and the three principal directions of their 

 activity (attraction, light- and heat-exciting undulations, 

 and electro-magnetic processes), the first division of the 

 present volume treated of the magnitude, figure, and 

 density of our planet ; its internal distribution of heat ; 

 and its magnetic condition. The above-named classes 

 of activity in the material universe (molecular and 

 mass-attraction or gravitation, light- and heat-exciting 



