318 



THE GEOLOGIST. 



Bronte. 



The change of clip in the inferior, medial, and nppemiosfc beds of 

 the Griannicola, and the convergence of the greenstone -dikes towards 

 the Trifoghetto centre are inexpUcable by the " crater of elevation 

 theory," but become plainly intelligible on the pi'iiiciple of a double 

 axis of eruption. Then, in the lower beds we perceive the lava 

 streams flowing away fi'om the old cone of eruption, and mingling in 

 the intercoUine space with the cur- 

 rents ejected from the Mongibello 

 crater, until, in the levelling pro- 

 cess thus being effected, the hori- 

 zontality of the succeeding lavas of 

 the middle portion occurs, and after 

 this the streams fi'om the existing 

 cone, flowing down in greater force 

 than those from Trifoglietto, gra- 

 dually overflowed and extinguished 

 it — the lavas which thus flowed 

 down presenting, of course, the oppo- 

 site dip to those below, or towards 

 the centre of Trifoglietto. 



The points of arg-ument next 

 brought forward are the want of 

 continuity in the older and modern 

 parts of Etna, and the truncation of 

 its summit : these are followed by a 

 discussion on the hypothesis of up- 

 heaval by injection. Geologis^^s who 

 assume that lava cannot congeal into 

 continuous stony layers on slopes 

 exceeding five or six degrees, must 

 unavoidably embrace the conclusion 

 that nine-tenths of the lava-beds 

 which constitute the nucleus of Etna, 

 and not a few also which overlie that 

 nucleus unconformably, were brought 

 into theu^ present position by me- 

 chanical forces, after the materials 

 of the mountain had accumulated 

 on nearly level gTound. 



M. Elie de Beaumont has sug- 

 gested that when new fissures are 

 produced during an eruption, radi- 

 ating fi'om tlie centre, and traversing 

 the nucleus of the mountain, the lava 



rising simultaneously to the rim of the highest crater would 

 fill such fissures, causing a tumefaction and distension of the whole 

 mass, and that thus a greater or less upheaval of the cone might 

 result. There is no actual data, however, for deciding that the 

 dyke-making process thus appealed to is usually attended by up- 



I Zoccalaro 



Zaffarana, 



