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Ch. XXVI.] 



TRUNCATION OF GREAT CONE. 



19 



anotlifir cone of still greater altitude in the same chain, called 

 Capac Urcii, was, according- to tradition, truncated a short 

 time before the conquest of America hj the Spaniards. It is 

 possible that when the lava is rising to the summit of such 

 cones the foundations of parts of the volcanic structure may 

 be undermined and melted, so that one part after another of 

 the walls of the highest crater niaj sink down before the 



ie STibjpM? principal escape of gas and the ejection of scoriae takes place. 



In the year 1792 a small circular tract called the Cisterna 

 (see Map, fig. 71), situated on the edge of the platform from 

 which the highest cone of Etna rises, sank down to the depth 

 of about 40 feet, leaving a chasm on all sides of which a 

 vertical section is now seen of alternating stony lavas and 

 scorise. It is conceivable, therefore, that parts of the area 

 of the Yal del Bove may, in like manner, have fallen in 

 during earthquakes ; but I think it probable that by far the 

 greater portion of the huge cavity was caused by explosions 

 of pent-up vapours escaping from subterranean fissures. 



tc a distant during one or more lateral eruptions connected perhaps with 



temp 

 have called the axis of Trifoglietto. 



-)/ Etna of 



cone. — What 



/ 



said of the first existence of 



Etna as a submarine volcano, the building up of the sub- 

 aerial part of the mountain by the pouring out of lava and 

 scoriae from two principal centres, the accompanying general 

 upheaval of the whole mass above the level of the sea, and 

 the probable origin of the Yal del Bove, has been entirely 



lounded on geological inferences from the internal structure 

 of the mountain. 



We may next turn to history and enquire what changes 

 are recorded to have taken place since the volcano was an 

 object of interest to the civilised world. 



Etna appears to have been in activity from the earliest 

 times of tradition ; for Diodorus Siculus mentions an eruption 

 which caused a district to be deserted by the Sicani before 

 the Trojan war. Thucydides informs us, that in the sixth 



War 



eam 



C 2 



