growths had long flourished on the earth 

 and been buried under sediments to be- 

 come beds of coal. Michell argued that 

 if a large body of water should be let 

 down suddenly upon one of these fires 

 a vapour would be produced, the quantity 

 and elastic force of which might be fully 

 sufficient to account for the origin of 

 earthquakes. He pointed out the fre- 

 quency of these concussions in volcanic 

 districts and, like the Wernerian geo- 

 gnosts, he connected the phenomena of 

 volcanoes with the same subterranean 

 fires, the vents and craters marking the 

 position of weaker portions of the outer 

 shell of the earth across which the vapour 

 generated below could force its way to 

 the surface, often carrying with it an out- 

 pouring of molten material. The energy 

 with which this escape was effected 

 appeared to him to be evident from the 

 vast size of the blocks of rock projected 

 during volcanic eruptions and the great 

 distances to which such masses of stone 



27 



