252 



In concluding this part of his memoir, Sir C. Lyell observes, that 

 the admission of a double axis, as explained by him, is irreconcile- 

 able with the hypothesis of "craters of elevation;" for it implies that, 

 in the cone-making process, the force of upheaval merely plays a 

 subordinate part. One cone of eruption, he says, may envelope and 

 bury an adjoining cone of eruption ; but it is obviously impossible 

 that one cone of upheaval should mantle round and overwhelm 

 another cone of upheaval. 



An attempt is then made to estimate the proportional amount of 

 inclination which may be due to upheaval in those parts of the 

 central nucleus of Etna where the dip is too great to be ascribed 

 exclusively to the original steepness of the flanks of the cone. The 

 highest dip seen by the author was in the rock of Musarra, where 

 some of the strata, consisting of scoriee with a few intercalated 

 lavas, are inclined at 47. Some masses of agglomerate and beds of 

 lava in the Serra del Solfizio were also seen inclined at angles 

 exceeding 40. Some of these instances are believed to be excep- 

 tional and due to local disturbance ; others may have an intimate 

 connexion with the abundance of fissures, often of great width, 

 filled with lava, for such dikes are much more frequent near the 

 original centres of eruption than at points remote from them. 

 The injection of so much liquid matter into countless rents may 

 imply the gradual tumefaction and distension of the volcanic mass, 

 and may have been attended by the tilting of the beds, causing them 

 to slope away at steeper angles than before, from the axis of erup- 

 tion. But instead of ascribing to this mechanical force, as many 

 have done, nearly all, or about four-fifths of the whole dip, Sir C. 

 Lyell considers that about one-fifth may, with more probability, be 

 assigned as the effect of such movements. 



The alleged parallelism and uniformity of thickness in the volcanic 

 beds of the Val del Bove, when traced over wide areas, is next con- 

 sidered, and the author remarks that neither in the northern nor 

 southern escarpments of the great valley, could he and his compa- 

 nion verify the existence of such parallelism. Examples of a marked 

 deviation from it are given, both in cliffs seen from a distance, and 

 in others which were closely inspected, even in cases where these last, 

 when viewed from* far off, appeared to contain regular and parallel 

 strata. 



