No. I. — Account of Mount Vesuvius. 191 



explosion of A. D. 79, the first recorded in history, and which 

 is imagined to have carried away the side of the mountain next 

 the sea, and to have left a flat space for the erection of a new 

 summit by subterranean action. The abrupt wall of the 

 Monte Somma lays open to us its internal constitution, and 

 shows that it is chiefly composed of lavas abounding in leu- 

 cite, and traversed by veins or dikes in various directions, 

 which have much puzzled geologists ; but appear to me suffi- 

 ciently easily accounted for by the supposition, that the pre-ex- 

 istent horizontal strata of lava were upheaved by internal ac- 

 tion, while this part of the mountain remained the crater, into 

 a dome-like shape, as the inclination of the strata actually 

 proves; but that, when the subterranean force ceased, the 

 mass being pressed downwards when nearly cool, it was tra- 

 versed by cracks or fissures diminishing in size from the bot- 

 tom to the top, as shown in the diagram, till by a new erup- 

 tion they were filled with a different kind of lava, forming the 

 dikes now observable. Similar dikes occur in the Lipari 

 Islands ; and in trap rocks they are very abundant. The 

 height of the ridge of Monte Somma is ,3703 feet above the 

 sea. At the foot of the interior precipice, between it and the 

 modern volcano, is the Atrio del Cavallo, a valley forming a 

 segment of a circle round the base of the cone, and which 

 has derived its name from travellers leaving their horses and 

 mules there when they prepare to ascend to the top on foot. 

 Its surface varies at different times, according to the condition of 

 the lava with which it is covered. At present it is extremely 

 rugged and desolate, as I have endeavoured to describe in my 

 account of an excursion up the mountains in this Journal, 

 (No. xiii. Art. 2.) being covered with the lavas of 1822, and 

 some older ones still perfectly sterile, with the exception of a 

 few lichens which grow in their cavities. At one part, near 

 the foot of the hill on which the hermitage is built, the lava of 

 1819 assumes the form of coils of ropes, which is the natural 

 consequence of a slaggy lava rolling slowly onward in waves, 

 and which is not peculiar to this volcano, as I have seen a spe- 

 cimen quite similar from the Peak of TenerifFe. Sir W. Ha- 

 milton, in his Carnpi Phlegrcei, has given a correct representa- 

 tion of this curious formation, which is called " Lava Corde." 



