Earthquakes and Volcanoes 



bodies, known as volcanic bombs. Occasionally 

 a very liquid lava may be caught by the wind, 

 and drawn out into delicate fibres, like spun 

 glass; this beautiful form is very abundant in 

 Kilauea, a volcano in Hawaii, one of the Sand- 

 wich Islands, where it is known as Pele's hair, its 

 name being borrowed from that of an old goddess 

 who was supposed to reside in the crater. Other 

 lavas again are vitreous, and strongly resemble 

 dark-coloured bottle-glass, when they pass under 



FIG. 52. Breached Volcanic Cones, Auvergne 



the name of obsidian. This kind of lava was 

 largely used by the ancient Mexicans for making 

 rude knives and other cutting instruments; and 

 a hill in northern Mexico, formerly worked for 

 this material, is still known as the Cerro de 

 Navajas (Spanish "Hill of Knives"). 



It often happens that the lava that wells up 

 in the pipe of a volcano, breaks by its sheer weight 

 through the rim of the crater, or even breaches 

 one side of the conical hill. Thus Fig. 52 repre- 

 sents a group of small extinct volcanoes in Cen- 

 tral France, showing cones which have been 

 broken through in this way. In some cases the 

 flanks of the cones are rent, and lava is then in- 

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