216 C. Lyell on the Formation of Volcanic Cones. 
-The structure of the nucleus of Etna, as exhibited in sections 
in the Val del Bove, is next treated of, and the doctrine Sis 
precipice at the head of the 
30° N. 7. €., towards 
two centres, originally hinted at by the late Mario Gemmellaro, 
had been worked out (unknown to Sir C, Lyell at the time of his 
visit) by Baron Sartorius von Waltershausen, and has since been 
the cone of Mongibello; and- 
the Val del Bove. The truncation of the S 
‘© is proved by the remains of the upper 
