No. I. — Account of Mount Vesuvius. 199 



ing the high character of this naturalist as an observer, and 

 the considerable advancement of science at the time in which 

 he wrote, I suspect he has here fallen into two, if not three, 

 material errors; 1st, that the lava is actually columnar. I 

 should hardly venture to place my opinion against that of 

 Breislak, were it not that the discrepancy may be explained by 

 the fact, that extensive excavations have been made in the lava 

 for a building stone, by which means its internal structure is 

 displayed in a way which Breislak could not have seen. 2d, 

 He expects to find crystalliform lava on account of the sudden 

 cooling of the lava below water, — an idea which is entirely ex- 

 ploded by the more recent discoveries of Dr Hutton and Dr 

 Hope, who have demonstratively proved that crystalliform 

 lavas or basalts can only be produced by very slow cooling ; 

 and hence, 3d, Huttonians have undertaken to prove that lava 

 cools slowest under water, (in order to reconcile theory with 

 facts, such as the one before us,) a position which Dr Dau- 

 beny* has ingeniously defended, but which I cannot even 

 touch upon here ; nor can I decidedly give my opinion on his 

 explanation, which, to say the least, appears somewhat para- 

 doxical. I shall conclude with saying, that I have not the 

 smallest doubt of the columnar arrangement of the lava where 

 it approaches the sea ; and I am convinced that excellent cabi- 

 net prismatic specimens might be procured from these quarries. 

 The structure of the Atrio del Cavallo has already been al- 

 luded to. There can be little doubt that it is composed to a 

 great depth of successive layers of lavas, volcanic conglome- 

 rate, and strata of ashes. It is nearly flat, and its breadth be- 

 tween the base of the cone and that of the Somma was, accord- 

 ing to the accurate measurements of Delia Torre f in the last 

 century, 2220 French feet, which cannot have greatly varied 

 to the present time. We have the means of examining its 

 structure best at the western end. There the hill named Canta- 

 roni, on which the hermitage stands, is entirely composed of 

 volcanic tufa, which, as we know it was raised from below, 

 evidently indicates the nature of the subsoil of this valley. In 

 fact, it would not require a word to illustrate so obvious a cir- 

 cumstance, as that the whole body of the volcano has been 



* Descriptions of Volcano*, p. 100. 



+ Storia del Vesuvia. 4to, Napoli, 1755, p. 5. v 



