131 TOWN GEOLOGY. [vi. 



itself between the bottom of tlie sea and the nether 

 fires. From each rushes an enormous jet of high- 

 pressure steam and other gases, which boils up through 

 the sea, and forms a cloud above ; that cloud descends 

 again in heavy rain, and gives out often true lightning 

 from its under side. 



But it does more. It acts as a true steam-gun, 

 hurling into the air fragments of cold rock rasped off 

 from the sides of the bore, and fragments also of 

 melted lava, and clouds of dust, which fall again into 

 the sea, and form there beds either of fine mud or of 

 breccia that is, fragments of stone embedded in 

 paste. This, the reader will understand, is no fancy 

 sketch, as far as I am concerned. I have steamed 

 into craters sawn through by the sea, and showing 

 sections of beds of ash dipping outwards and under 

 the sea, and in them boulders and pebbles of every 

 size, which had been hurled out of the crater ; and in 

 them also veins of hardened lava, which had burrowed 

 out through the soft ashes of the cone. Of those lava 

 veins I will speak presently. What I want the reader 

 to think of now is the immense quantity of ash which 

 the steam-mitrailleuse hurls to so vast a height into 

 the air, that it is often drifted many miles down to 

 leeward. To give two instances : The jet of steam 

 from Vesuvius, in the eruption of 1822, rose more than 

 four miles into the air; the jet from the Souffriere of 

 St. Vincent in the West Indies, in 1812, probably rose 

 higher; certainly it met the N.E. trade-wind, for it 

 poured down a layer of ashes, several inches thick, 

 not only on St. Vincent itself, but on Barbadoes, 

 eighty miles to windward, and therefore on all the sea 

 between. Now let us consider what that represents 



