The Virunga Volcanoes 



The earth, being a live world and not a dead one, must 

 breathe ; volcanoes may, therefore, also be described as the 

 " breathing places " of the globe, where the pent-up gases, 

 formed beneath the world's crust, may escape. 



To go a httle deeper into the subject, the earth* must 

 be considered as a gradually cooling, and consequently con- 

 tracting, spherical mass with a comparatively shallow outer 

 crust of water-logged earth and stone, beyond which the 

 interior is composed of either soUd or molten rock. 



Now it is easy to understand that all cooling bodies 

 contract. Therefore on this account, and also in part 

 helped by the continual shifting of masses of the earth's 

 surface by the action of water, pressure and strainf are set 

 up resulting in crustal convulsions and earthquakes. The 

 globe, therefore, on which we live, is continually altering, 

 being raised up in some parts, whilst in others it subsides. 

 Thus are the fissures and cross-fissures formed which, when 

 reaching down to a lake or " pocket " of molten lava, become 

 the pipes along which this lava may perhaps reach through 

 to the surface. 



I say " perhaps," for the fissure may be there and the 

 molten lava at the bottom of it, but it won't spurt forth 

 " on its own," so to speak. It must have some driving 

 force behind it and obviously some agent which is strengthened 

 by repression. This force is water, and steam (which is water 

 vaporised). Likewise if the water is withdrawn from a volcano 

 it will cease to be active. 



• The earth is assumed to have been originally a burning incandescent 

 mass. 



t Isostasy : or the endeavour of a rotating body after distortion to assume 

 a form in which it is again in equilibrium ; has also been brought forward as 

 a potent factor in producing movements and fissures in the earth's crust. . 



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