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Show 84 NEWER PLIOCENE PERIOD· [Ch. VII. depth that they expose to view a great part ~f th: structure of the entire mass, which, in the Val del Bove, IS lald 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-currents 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 escarpment 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 Dove to the inferior borders of the woody region, fully answers such expectations. 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 discovct· indications of disturbances, occasioned by the passage of lava from below, and the successive inhumation of lateral cones. Val di C'alanna.-On leaving Zaffarana, on the borders of the fertile region, we enter the ravine-like valley of St. Giacomo, and sec on the north side, or on our right as we ascend, Ch. VII.] VAL DI CALANNA. 85 rising ground composed of the modern lavas of Etna. On our. l~ft, a lofty cliff, wherein a regular series of beds is cxlnb1ted, composed of tuffs and lava' s' descend1' ng w1· t 11 a gen~le inclination to~ards the sea. In this lower part of the sectwn there are no Intersecting dikes nor any s1' (J'ns f · • • • ' 0 o mmor con:s mterfermg with the regular slope of the alternating vol-camc products. If we then pass upwards through a defile, ca11cd the ' Portello di Calanna,' we enter a second valley, that of Calanna, resembling the ravine before mentioned, but wider and much deeper. Here again we find ' on our d(0J 'ht , many currents of modern lava, piled one upon the other, and on our le~t .a continuation of our former section, in a perpendicular cliff from four hundred to five hundred feet high. As this lofty wall sweeps in a. curve' it has very much th e appearance of the .escarpment w~1c~1 Somma presents towards Vesuvius, and this resemblance 1s mcreased by the occurrence of two or three vertical dikes which traverse the gently-inclined volcanic beds. When I first beheld this precipice, I fancied that I had entered a lateral crater, but was soon undeceived b d . . I ' y . 1scover~ng t 1at on all sides, both at the head of the valley, m the lull of Zocolaro, and at its side and lower extremity ~he dip of the beds was always in the same direction, all slant~ mg to the east, or towards the sea, instead of sloping to the north.' east, and south, as would have been the case had they constituted three walls of an ancient crater. It is not difficult to explain how the valleys of St. Giacomo and Calanna odginated, when once the line of lofty preci.p.ic es on the nor.t h side of them had been formed · M any l ava-cur-rcnts flowmg down successively from the ]1 1•g , l1 er regw· ns 0 f Etna, along the foot of a great escarpment of volcauic rock have at length been turned by a promontory at the head of th; ~alley of Calanna, which runs out at right angles to the g t lme of . . . rea preciplCes. This promontory consists of the hills called Zocolaro and Calann a, an d o f a 1'1· a ge o f m. feri.O r height which connects them. (See diagram No. 18.) |