Ch. XIII. ] EASTERN BASE OF MOUNT ETNA. 191 



In 1857 and 1858, when I revisited Sicily, I obtained, through the 

 kindness of Dr. Aradas, of Catania, a much larger" number of species 

 from the same localities, which confirmed the conclusions formerly ar- 

 rived at as to the age of these deposits. Out of 142 shells, all but 

 eleven proved to be identical with species now living. Some few of 

 these eleven shells may possibly still linger in the depths of the Med- 

 iterranean, like Murex vaginatus, fig. 141, p. 190. The last-mentioned 

 shell had already become rare, when the sub-Etnean deposits were 

 formed. On the whole, the modern character of the testaceous fauna 

 under consideration is expressed not only by the small proportion of 

 extinct species, but by the relative number of individuals by which 

 most of the other species are represented, for the proportion agrees 

 with that observed in the present fauna of the Mediterranean. The only 

 extinct shell which can be said to be common is Buccinum semistria- 

 ium; B. mUsivum comes next in abundance. The rarity of the other 

 nine is such as to imply that they were already on the point of dying 

 out, having flourished chiefly in the earlier Pliocene times when the 

 Subapennine strata were in progress. 



Yet since the accumulation of these Newer Pliocene sands and clays, 

 the whole cone of Etna, 11,000 feet in height and about ninety 

 miles in circumference at its base, has been slowly built up ; an opera- 

 tion requiring many tens of thousands of years for its accomplish- 

 ment, and to estimate the magnitude of which it is necessary to study 

 in detail the internal structure of the mountain, and to see the proofs 

 of its double axis, or the evidence of the lavas of the present great 

 centre of eruption having gradually overwhelmed and enveloped a 

 more ancient cone, situated 3^- miles to the east of the present one. 

 We ought also to satisfy ourselves, as we may easily do, that in breadth 

 and thickness each of the older lavas did not exceed in their average 

 volume the products of single outpourings of historical times. In spec- 

 ulating, moreover, on the lapse of bygone ages, we must take into ac- 

 count the different dates and varying composition of the dikes up 

 which the lavas poured, whether belonging to the eastern or western 

 axis, and the manner in which one set of dikes cuts through an older 

 one ; also, the vast denudation to which the Yal del Bove, or deep 

 valley, on the eastern flank of the mountain, bears testimony ; and, 

 lastly, the gradual upheaval above the level of the sea of some of the 

 submarine rocks first formed, and the origin of many hundred minor 

 cones, the result of lateral outbreaks during the most modern phase of 

 eruption. These and other observations must be made, before the 

 prodigious antiquity of the Newer Pliocene marine strata above de- 

 scribed can be fully appreciated.* 



It appears that while Etna was increasing in bulk by a series of 

 eruptions, its whole mass, comprising the foundations of subaqueous 



* See a Memoir on the Lavas and Mode of Origin of Mount Etna, by the Author, 

 Phil. Trans., 1858. 



