Mr Simond on the Eruptions of Mount uEtna. 313 



208,000 houses, and each house to contain 5000 cubic feet of 

 walls. This same eruption of 1669 destroyed the habitations 

 of twenty-seven thousand people. 



The region south of ^tna, extending towards Cape Pachi- 

 no nearly one hundred miles, exhibits often to a great depth 

 shelly calcareous strata alternating with what the Abbate Fer- 

 rara calls ancient lava, and the low grounds are full of marine 

 and argillaceous deposits. The base of the mountain, as far 

 as can be ascertained, is of the same nature. From all these 

 facts the same learned writer infers, that his ancient lava is of 

 submarine formation, the stupendous superstructure having 

 been reared after Sicily had become dry land. This ancient 

 lava, however, visible in many places, and particularly at La 

 Motta, very near the volcano, is in fact basalt ; a substance 

 which, although it resembles lava, and probably was likewise 

 once fluid through the agency of fire, differs too much, and 

 especially by its abundance, to have the same origin and be of 

 the same formation as lava. 



Mtna, although situated nearly in the direction of the great 

 chain of the Appennines, stands insulated. It is a truncated 

 cone about ninety miles in circumference at the base and ten 

 miles at top, * where there it is a level plain round the mouth 

 of the volcano. That mouth in great eruptions occupies the 

 whole plain, while at other times it is no bigger than a man's 

 head, as I have heard it described here. Being the safety- 

 valve of the boiler, it cannot be quite closed without dreadful 

 consequences. In great eruptions there is certainly no possi- 

 bility of approaching to ascertain the state of the plain ten miles 

 in circumference just described ; but as it is afterwards found 

 to have undergone a total change, the cone upon it also being 

 rebuilt often in another place, there can be no doubt that du- 

 ring an eruption this lid of the boiling caldron comes off en- 

 tirely. When the activity of the fire begins to decline, the 

 lava instead of boiling quite over swells no higher than the 

 mouth of the crater, and there hardening quickly by its con- 

 tact with the open air, forms a leyel surface or new plain like 



* ^tna being only 10,200 feet, or nearly two miles in height, while at 

 the base it is thirty miles in diameter, its ascent apparently steep is in re- 

 ality very gradual. 



