94 NEWER PLIOCENE PERIOD. [Ch. VII. 



floods do occasionally sweep down the flanks of Etna when 

 eruptions take place in winter, and when the snows are melted 

 by lava. 



Many of the angular fragments may have been thrown out 

 by volcanic explosions, which, falling on the hardened sur- 

 face of moving lava-currents, may have been carried to a con- 

 siderable distance. It may also happen, that when lava ad- 

 vances very slowly, in the manner of the flow of 1819, described 

 in the first volume*, the angular masses resulting from the 

 frequent breaking of the mass as it rolls over uipon itself, may 

 produce these breccias. It is at least certain, that the upper 

 portion of the lava-currents of 1811 and 1819, now consist of 

 angular masses to the depth of many yards. 



D'Aubuisson has compared the surface of one of the ancient 

 lavas of Auvergne to that of a river suddenly frozen over by 

 the stoppage of immense fragments of drift-ice, a description 

 perfectly applicable to these modern Etnean flows. 



* Chap. xxi. 



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