iS 



«tlh 



s < 



^ 





'^ of 



e 



(1 *1 In- 

 ns 



ca 



and 



(fori 



m 



? 



1 found 

 called 



ne are 

 m area 



iber of 



ie same 

 lerated 



1; and 

 and in 

 e rear 



Some 

 f these 

 Clients 

 us ex- 

 ilv, or 



ducts : 



dis- 



.arth' 



a 



Ch. XXV.] 



HYPOTHESIS OF ELEVATION CEATEES 



6 



Co 



jj; would have been readily admitted that these, or a much 

 rreater variety of substances, had been sublimed in the 



g 



crevices of lava, just as several new earthy and metallic 

 compounds are known to have been produced by funieroles, 

 since the eruption of 1822. 



At the fortress near Torre del Greco a section is exposed, 

 fifteen feet in height, of a current which ran into the sea ; 

 and it evinces, especially in the lower part, a decided tendency 

 to divide into rude columns. 



encircling 



the 



Mr. Scrope mentions that, in the cliffs 

 modern crater of Vesuvius, he saw many currents offering a 

 columnar division, and some almost as regularly prismatic as 

 any ranges of the older basalts ; and he adds, that in some 



the spheroidal concretionary structure, on a 



large 



scale, 



was equally conspicuous. Brieslak also informs us that, in 

 the siliceous lava of 1737, which contains augite, leucite, 

 and crystals of felspar, he found very regular prisms in a 

 quarry near Torre del Greco ; an observation confirmed by 

 modern authorities. 

 Hypothesis of elevation craters not applicable 



to 



\j 



Monte 

 Somma or to Vesuvius. — It has been imagined by MM. Yon 



Buch and Dufrenoy, that a large part of the tufaceous strata 



which rise in Somma to more than half the height of the 



mountain are of submarine origin, an opinion which I shall 



show to be quite untenable. The same writers, as well as 



M, E. de Beaumont, have also taught that, the sheets of 



lava which we see in the great section of Somma laid open 



in the Atrio, could not originally have been inclined at angles 



of more than four or five degrees, so that four-fifths of their 



present slope must be due to their having been subsequently 



heaved up and tilted. Their original approach to horizontality 



was inferred from the compact structure of many of the beds, 



as well as their supposed parallelism and continuity in the 



line of their strike. M. E. de Beaumont, in particular, has 



contended that if they had run down a greater inclination 



than four degrees, and still more decidedly if they had poured 

 clown 



a 



slope 



exceeding twenty degrees, 



they would have 



consisted not of broad sheets of solid rock, but of narrow 

 streams of porous lava and seorise. 



