a 



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■fent 







^•^■*WJi 



iof that name, 



y 



f flowiDgnxndtt 



'ed the plat 

 irrent c, i 



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"Htf 



P'^r' 



^ 



.:uj» 





0«»* f Irer t^ 



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tf 



tbe 



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tor? 



t_ ;^ 



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Ider 



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Ch. XXVI.] 



IIS^CLINED LAVA OF CAVA GEANDE. 



\5 



its predecessors of 1811 and 1819^ turned round the promon- 

 tory formed by the Hill of Calanna^ and moving right onwards 

 has been piled up on the left side of the Valley of Calanna so 

 as to heighten its boundary wall without flowing down into it. 

 Both the lavas of 1819 and 1852 had been covered origi- 

 nally in every part where they congealed on the face of the 

 steep precipice with the usual scoriaceous crust. But this 

 crust, about three feet thick, had been washed off by rain 

 at several places, and had exposed to view a solid and con- 

 tinuous stony layer below. The rock is somewhat vesicular, 

 and contains crystals of felspar, augite, and olivine, with 

 some titaniferous iron. As it is inclined at angles of from 

 35° to SO"", it affords a striking refutation of the doctrine that 



from 



to 5 



/ 



Grande. — Amon 



other examples 



attesting the erroneousness of the notion just alluded to, I 

 maj call attention to another cascade of lava the internal 



clearly exposed to view. On 



more 



the eastern flank of Etna, north of Milo, is a deep and 



Map 



^1), 



narrow guUey called the Cava Grande 



which, although usually dry, has been 



through successive beds of ancient lava and scoriae by the 



waters of occasional floods, which cascade over a perpen- 



entirely excavated 



dicular 



form 



the ravine. The torrent is gradually cutting its way back- 

 wards, and thus adding to the length of the narrow valley. 

 I witnessed, October 1857, several avalanches of sand and 

 stones loosened from the terminal cliff by the heavy rains of 

 the preceding day. The boundary walls of the opposite sides 

 of the Cava Crande are 220 feet high, in part vertical, in 

 part sloping at angles of between 38° and 65°. 



In the year 1689, a lava stream descended from the Yal 

 del Bove in a direction nearly parallel to the Cava Grande, 

 but a portion of its left side was precipitated into the ravine 

 in the manner represented at a' a' a' in figure 8 7. 



In addition to the retrogressive excavation of the head of 

 the ravine caused by the torrent before mentioned, the steep 

 boundary precipices are also undergoing constant waste, by 



means 



D 2 



