320 



THE GEOLOGIST. 



crystalline lavas, whether trachytic or doleritic, whether slightly or 

 steeply inclined, been in great part intrusive, they would have altered 

 the tuffs as much ahove as below them. Moreover, they must have 

 given rise to innumerable faults ; for while they vary in thickness 

 from 3 to 60 feet, they are not persistent for indefinite distances, but 

 often thin out rapidly in both directions. They ought therefore, had 

 they been injected, to have lifted up the incumbent deposits partially, 

 so as to give rise to many conspicuous faults. For these reasons, I 

 can not adopt the conclusion that the upheaval of Etna has been 

 largely due to the injection of lavas in sheets parallel or conformable 

 to the tuffs and fragmentaiy materials." 



M. Elie de Beaumont in his celebrated essay on Mount Etna 

 insists on the uniformity in thickness and parallelism of the many 

 hundreds of lava-beds which are presented on the escarpments of 

 the Val del Bove, and on their continuity for great distances, as facts 

 confirmatory of the doctrine of their original horizontality and sub- 

 sequent upheaval into their present positions, referring their occa- 

 sional steep inclinations to their liability to be bent together, like 

 the regular sedimentary strata which have undergone flexures in 

 mountain-chains. This assertion has not escaped the keen observa- 

 tion of Sir Charles Lyell, and consequently we have a portion of 

 liis paper devoted to the evidence of pseudo-parallelism and the want 

 of uniform thickness of the beds forming the escarpments of the Val 

 del Bove. A conspicuous selected case of want of uniformity in 

 thickness of stony layers in the northern escarpment — one bed 



Lign, 2.— Non -parallel Lavas. Want of Uniformity in Thickness of Stony Layers in 

 Northern Escarpment of the Val del Bove. 



attaining forty -feet in its thickest part — and instances of non-parallel 

 strata to the south of Einocchio Inferiore, and at the Serradel Solfizio, 

 with an example of curvatures in the lavas of Zoccolaro effectually 



Lign. 3.— Cm-vatures of the Lavas of Zoccalaro. 



dispose of this point, and leave remaining only the easy task of 

 proving the analagous form and arrangement of the ancient and 

 modern lavas. 



The third part of Sir Charles's paper is devoted to the relation of 

 the volcanic rocks of Mount Etna to the associated alluvial and 

 modci-n tertiary deposits of Giarre. 



