84 NEWER PLIOCKNE PERIOD. [Ch. VII. 



depth that they expose to view a great part of the structure of 

 the entire mass, which, in the Val del Bove, is laid open to the 

 depth of from four thousand to five thousand feet from the 

 summit of Etna. The geologist thus enjoys an opportunity 

 of ascertaining how far the internal conformation of the cone 

 corresponds with what he might have, anticipated as the result 

 of that mode of increase which has been witnessed during the 

 historical era. 



It is clear, from what we before said of the gradual manner 

 in which the principal cone increases, partly by streams of lava 

 and showers of volcanic ashes ejected from the summit, partly 

 by the throwing up of minor hills and the issuing of lava-cur- 

 rents on the flanks of the mountain, that the whole cone must 

 consist of a series of cones enveloping others, the regularity of 

 each being only interrupted by the interference of the lateral 

 volcanos. 



We might, therefore, have anticipated that a section of Etna, 

 as exposed in a ravine which should begin near the summit and 

 extend nearly to the sea, would correspond very closely to the 

 section of the ancient Vesuvius, commencing with the escarp- 

 ment of Somma, and ending with the Fossa Grande; but with 

 this difference, that where the ravine intersects the woody 

 region of Etna, indications must appear of changes brought 

 about by lateral eruptions. Now the section before alluded to, 

 which can be traced from the head of the Val del Bove to the 

 inferior borders of the woody region, fully answers such ex- 

 pectations. We find, almost everywhere, a series of layers of 

 tuff and breccia interstratified with lavas, which slope gently to 

 the sea, at an angle of from twenty to thirty degrees ; and as 

 we rise to the parallel of the zone of lateral eruptions, and still 

 more as we approach the summit, we discover indications of 

 disturbances, occasioned by the passage of lava from below,, 

 and the successive inhumation of lateral cones. 



J'fd dl CfdtniiHt. On leaving Zaffarana, on the borders of 

 the fertile region, we enter the ravine-like valley of St. Gia- 

 como, and see on the north side, or on our right as we ascend; 



