14 



ETNA. 



[Ch. XXVI. 



dikes of different ages sliould be so nearly vertical as 



tliey 



one 



are found to be. But as I have dwelt so long on this sub'-'eot 

 on a former occasion^ I w^ill merely say liere^ in favour of th 

 theory of eruption as opposed to that of upheaval, that 

 cone formed by eruption may and often does embrace and bnrv 

 a contiguous cone of older date and of similar origin ; whereas 

 a cone of upheaval, even if we grant that the volcanic forces 



ever give rise to such a structure^ cannot be conceived to 



envelope an older cone. 



Want of parallelism in the ancient lavas. — It will be useful 

 however, to point out in detail some features in the shape 



Fig. 73. 



Stony layers in the northern escarpment of the Val delBovein the Serra di Cerrita 

 part of the Coneazze (see Map, fig. 71), where the precij)ice is 1,000 feet hioh. 



a. Vertical section of rock 40 feet. 

 &, c. Beds to the westward in the same 

 plane as the thickest part of a. 



d. Same bed as a thinning out westwardto 

 a thickness of 4 or 5 feet at a distance of a 

 few hundred yards from a. 



and structure of the beds which are intersected in the chffs 

 of the Yal del Bove^ in order to show that they are not uni- 

 form in thickness, and that they by no means preserve eyerj- 

 where that perfect parallelism to each other which has been 

 ascribed to them. They present, it is true, to the eye, a 

 great appearance of regularity when viewed as a whole and 



from a distance, but when 



Fig 74. 



mor 



are found to be variable, 

 both in thickness and in 

 their dip, as much so as we 

 have any right to expect in 



Ison-parallel beds of stony lava iu the Con- curreut^ xvhiVh h^ve flowed 



down the sides of a steeply 



cazze, or part of the northern escarpment 

 of the Val del Bove. 



Vertical distance from a to 6 about 60 feet. In- slopiUg COUO llkc Etna from 

 coherent tuffs and scorige intervene between the '^olid • j I'Un 



beds here figured. ^ '*'^''^ souic oponuig at or near the 



summit. The annexed dia- 

 grams will explain the appearance of the lavas and scoria 

 at many points in the north and south walls of the Val del 

 Bove, where they are laid open to view in vertical sections. 



\ 



4 

 1 



i 



im 



1 



&■ 



y 



\'^' 



M 



i 







in sncc'' 



the «^^' 

 sloping 



luark? 



tJ 



ffe t)eli< 



running 

 directioi 



ginal c( 

 currents 



every « 

 pect the 

 tiiiiious 

 miles, 

 dip, eve' 

 to 20° 



is no r( 

 cludino-, 



Iiave bee 



I 



maj 



cones lai 



( 



the 



graiK 



eiHbited 



r, 



