VOL. LX.] PHILOSOPHICAL TRANSACTIONS. 5 



the Catania side, and many others on the other side of the mountain, all of a 

 conical form, and each having its crater ; many with timber trees flourishing 

 both within and without their craters. The points of those mountains, that he 

 imagined to be the most ancient, are blunted, and the craters of course more 

 extensive and less deep than those of the mountains formed by explosions of a 

 later date, and which preserve their pyramidal form entire. Some have been so 

 far mouldered down by time as to have no other appearance of a crater than a 

 sort of dimple or hollow on their rounded tops, others with only half or a third 

 part of their cone standing ; the parts that are wanting having mouldered down, 

 or perhaps been detached from them by earthquakes, which are here very fre- 

 quent. All however have been evidently raised by explosion ; and he believes, 

 on examination, many of the whimsical shapes of mountains in other parts of 

 the woild would prove to have been occasioned by the same natural operations. 

 Sir W. observed that these mountains were generally in lines or ridges; they 

 have mostly a fracture on one side, the same as in the little mountains raised by 

 explosion on the sides of Vesuvius, of which there are 8 or Q. This fracture is 

 occasioned by the lava's forcing its way out. Whenever he shall meet with a 

 mountain, in any part of the world, whose form is regularly conical, with a 

 hollow crater on its top, and one side broken, he will be apt to decide such a 

 mountain s hayine; been formed by an eruption, as both on Etna and Vesuvius . 

 the mountams formed by explosion are without exception according to this de- 

 scription. They looked into ii,^^ jjreat crater, which is about 2^ miles in cir- 

 cumference ; they did not think it s..f, tr, go round and measure it, as some 

 parts seemed to be very tender ground. The ms.a, ^f ^^^ ^^^^^^^ ^^-^^ -^ j^_ 

 crusted with salts and sulphurs like that of Vesuvius, is n. ^^^^ f^^^ ^^ ^^ j^_ 

 verted hollow cone, and its depth nearly answers to the heigiu r ^u y^.i 

 mountain that crowns the great volcano. The smoke issuing abundantly i.^^ 

 the sides and bottom, prevented their seeing quite down ; but the wind clearing 

 away the smoke from time to time, they saw this inverted cone contracted almost 

 to a point. The air was so very pure and keen in the whole upper region of 

 Etna, and particularly in the most elevated parts of it, that they had a difficulty 

 in respiration, and that independent of the sulphureous vapour. At the foot of 

 Etna, the 24th, the quicksilver stood at 27 degrees 4 lines, and the 26th, at the 

 most elevated point of the volcano, it was at 18 degrees 10 lines. The ther- 

 mometer, on the first observation at the foot of the mountain was at 84 degrees, 

 and on the second at the crater at 56. The weather had not changed in any 

 respect, and was equally fine and clear, the 24th and 26th. He believes that the 

 perpendicular height of mount Etna is something more than 3 Italian miles. 



After having passed at least 3 hours on the crater, they descended and went to 

 a rising ground, about a mile distant from the upper mountain just left, and saw 



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