1859.] on the Conical Form of Volcanoes, 131 



ascribe the whole elevation to a force acting from below, as it would have 

 been if the uppermost layers of each volcanic mountain could be assumed 

 to be of marine origin. In opposition to such a doctrine, Sir C. Lyell 

 maintains that mechanical force has nowhere played such a dominant 

 part in the cone-making process as to warrant our applying any other 

 term save that of " cones of eruption " to volcanic mountains in 

 general. 



In conclusion, the lecturer gave a brief sketch of the series of geolo- 

 gical events which he supposed to have occurred on the site of Etna 

 since the time of the earliest eruptions, events which may have required 

 thousands of centuries for their development. The first eruptions are 

 believed to have been submarine, occurring probably in a bay of the 

 sea, which was gradually converted into land by the outpouring of lava 

 and scoriae, as well as by a slow and simultaneous upheaval of the 

 whole territory. The basalts, and other igneous products of the 

 Cyclopean Islands were formed contemporaneously in the same sea, the 

 molluscous fauna of which approached very near to that now inhabiting 

 the Mediterranean ; so much so, that about nineteen -twentieths of the 

 fossil species of the sub-Etnean tertiary strata still live in the adjoin- 

 ing seas. Hence, as that part of Etna which is of subaerial origin is 

 newer than such fossils, the age of the mountain is proved to be, 

 geologically speaking, extremely modern. During the period when 

 the volcano was slowly built up, a movement of upheaval was gradually 

 converting tracts of the neighbouring bed of the sea into land, and 

 causing the oldest volcanic and associated sedimentary strata to rise, 

 until they reached eventually, a height 1200 feet (and perhaps more) 

 above the sea-level. At the same time the old coast-line, together with the 

 alluvial deposits of rivers, was upraised, and inland cliffs and terraces 

 formed at successive heights. The remains of elephants, and other 

 quadrupeds, some of extinct species, are found in these old and up- 

 raised alluviums. Fossil leaves of terrestrial plants also, such as the 

 laurel, myrtle, and pistachio, of species indigenous to Sicily, have been 

 detected in the oldest subaerial tuffs. At first the cone of Trifoglietto, 

 and probably the lower part of the cone of Mongibello, was built up ; still 

 later the cone last-mentioned, becoming the sole centre of activity, over- 

 whelmed the eastern cone, and finally underwent in itself various trans- 

 formations, including the truncation of its summit, and the formation 

 of the Val del Bove on its eastern flank. Lastly, the phase of lateral 

 eruptions began, which still continues in full vigour. 



[C. L.] 



