218 C. Lyell on the Formation of Volcanic Cones. 
points remote from them. The injection of so much liquid ee 
into countless rents may imply the gradual tumefaction a 
tention of the volcanic mass, and may have been attended by the 
tilting of the beds, causing them to slope away at steeper a 
than before, from the axis of eruption. But instead of aseri 
to this mechanical force, as many have done, nearly all, or Re 
four-fifths of the whole dip, Sir C. Lyell opnkiags that about one- 
fifth may, es more probability, be assigned as the effect of such 
movem : 
- The alleged parallelism and uniformity of thickness in the 
volcanic beds of the Val del Bove, when traced over wide areas, 
is next considered, and the author remarks that neither in the 
northern nor southern escarpments of the great valley, could he 
and his companion verify the existence of such parallelism. 
Soclerples ‘of a marked deviation from it are given, both in clifis 
seen from a distance, and in others which were closely i i 
even in cases where these last, when viewed from far off, appeared 
to contain regular and parallel strata. : 
The direction and position of the dikes in the Val del Bove is, 
then spoken of, both in reference to the two ancient centres 
intersected beds. In regard to the arrangement also of the 
cones of eruption, the question is entertained, whether they are 
disposed in linear zones , or are in some degree independent © of 
the great centre of Mongibe llo. 
The origin of the Val del Bove fas been variously ascribed i 
to engulfment, explosion, and aqueous erosion. Admitting the 
probable influence of the first two causes, the author calls atten- 
tion to the positive evidence in favor of aqueous denudation 
afforded by the accumulation of alluvium in the lower country 
at the eastern base of Etna between the Val del Bove and the 
sea. This rudely stratified deposit, 150 feet — ny Ri ral 
miles in length and breadth, contains at Giarre, Mangan Riposto 
and other places, fragments, both rounded and angular, oe all a a 
; ancient and modern, occurring in the escarpments fe 
Val del Bove, and it implies the continuance there for ages of 
powerful aqueous erosion. The alluvium of Giarre is therefore 
supposed to bear the same relation to the Val del Bove that the 
eS. to t 
, are of su 
d to him by MM. 
