324 Mr, Lohlcy^s Lecture on Vesuvius, 



wall of the pjreat crater whicli existed previous to the renewal of the 

 activity of the volcano in 79, is composed entirely of volcanic pro- 

 ducts. It is not, however, like the walls of the craters of the 

 Phlegraean fields, made up of tuff; but is formed, like the modern 

 cone of Vesuvius, of a series of beds of lava alternating with layers 

 of scoriae and ashes, and traversed by dykes of compact dolerite. 

 The lavas of the Pre-historic volcano differ considerably from those 

 of modern times, the latter containing little free leucite, and not 

 more than six or seven other minerals ; while the lavas of Somma 

 contain a great abundance of leucite, in fine trapezohedral crystals, 

 as well as a large number of associated minerals. The beds of lava 

 and scoria3 composing Monte Somma, overlie the rock of which the 

 whole of the lower portion of the mountain is composed, and which 

 is a soft, straw-coloured, volcanic tuff, similar to the rock so much 

 exposed about the city of Naples, and through which is excavated 

 the great grotto of Posilipo. This is evidently the oldest product 

 of the volcano, and has, doubtless, in part at least, been deposited 

 under water, from the fact of several species of marine Mollusca 

 having been found in the tuff of this neighbourhood. The funda- 

 mental rock of the district is the Apennine limestone, which is of 

 Cretaceous age, and on this the whole mountain reposes. 



Kesina, one of the populous towns at the foot of the mountain, 

 and on the shore of the bay, is the usual starting place when the 

 ascent of the mountain is made. This town is built upon the lava 

 of 1631, which overlies the bed of tuff in which Herculaneum is 

 entombed. After leaving Resina, the path traverses highly culti- 

 vated and very fertile vineyards and gardens, in which the famous 

 wine " Lachryma Christi " is produced. The land owes its great 

 fertility to the felspathic matter derived from the decomposition of 

 the underlying lavas. After ascending gradually for about two 

 miles, the lava of 1858 is reached, and the scene is entirely changed; 

 for from this point to the summit there is not a trace of vegetation. 



The appearance of the surface is very extraordinary, from the gro- 

 tesque and varied forms the lava has assumed in cooling. The 

 colour of the recent lavas is, in some places, black; in others, a 

 dark brown ; and the surface is exceedingly rough and diflicult to 

 walk over. The ridge of the Crocelle rises out of this sea of lava, 

 and on its summit stand the Hermitage and Observatory. 



From the Crocelle the observer looks over that part of the moun- 

 tain down which the red hot lava flowed during the recent 

 eruption. The lava of this year, it appears, issued from the top of 

 the old cone, and descended its side for some time in a splendid 

 fiery stream ; but this stream becoming covered, by cooling, with 

 a crust of hardened lava, the fluid was not seen until it had 

 reached the base of the cone, when it came to the surffxce, issuing in 

 small streams at various points. These streams run slowly and 

 noiselessly along, losing their brightness very quickly, soon becoming 

 covered with scorias, and, after flowing about a hundred yards, losing 

 their fluidity and breaking up into cindery masses, which form 

 ridges not unlike unfinished railway embankments. After passing 



