LAVA STEAM-DRIVEN. 89 



seen to take place in the Geysers, in which it can 

 even be caused by throwing stones into theirmouths. 

 Since the discharge of melted rocks is always 

 attended with outbursts of steam, we may assume 

 that a great deal of steam must come up, mixed 

 with the liquid stone, through the vent-holes of the 

 volcanoes ; and that for this reason the upheaved 

 column of lava has far less weight, than we might 

 suppose it to have from its density when solid, 

 although its mass, even in tins state, is thoroughly 

 filled with bubbles. Besides, it is likely that the 

 lava of volcanoes, that are still active, comes from 

 a much less depth than might be imagined from its 

 melting temperature, which, according to Bischof, 

 is between the melting-points of silver and of 

 copper. For it is very possible that the water that 

 penetrates into the deepest clefts, and is there 

 brought up to a red heat (hi places, where by the 

 excess of pressure from without, or by the narrow- 

 ness of the outlets, the formation of steam may 

 be hindered or retarded), imparting its heat to 

 the strata lying above, and gradually melting the 

 most fusible parts, may thus at last bore a passage 

 for itself, through which it rushes, carrying with it 

 the melted mass, and the loosened earth. 



According to this view, volcanoes are, as Keug 

 vox Nidda long ago expressed it, nothing but 

 huge intermitting springs, from which, instead of 

 water, liquid lava flows. 



