322 



THE GEOLOGIST. 



more than one centre, and pierced by a succession of dikes, was 

 already complete before the Yal del Bove began to be formed." 



The alluvial formation on which Giarre and some other towns on 

 the coast are bnilt, attests the removal, at some unknown period, of a 

 vast quantity of stony fragments from that part of Etna which lies 

 immediately in the direction of the Val del Bove ; and if it could be 

 sho^vn that this transported matter came down from that great 

 vallev, it would go far to prove that the abstraction of the missing- 

 rocks was for the most part effected by aqueous agency. On ex- 

 amination it actually appears that the portion of this deposit, — which 

 consists of coarsel}^ stratified materials, with rounded and angular 

 blocks some nine feet in diameter, but without striations or scratches 

 like the " glacial di'ift" — opposite to the Val del Bove is conspicuous 

 beyond the rest for its volume, and by being exclusively composed of 

 the wi'eck of the volcano itself, the blocks being of trachyte, basalt, 

 dolerite, grey-stone, and indeed of every variety of rock met with in 

 the Yal del Bove ; some being evidently derived from dikes. 



As usual. Sir Charles provides against attack by combatting the 

 probable objections likely to be made to his notions. " It may," he 

 says, " perhaps be suggested that the deposit at Giarre and Mangeno 

 might have been swept down by rivers from the old cone when it 

 was still entire, and before the caldera originated, in favour of which 

 theory it might be urged that in the Yal del Bove at present we dis- 

 cover no action of running water capable of causing extensive 

 denudation ; also that we may well imagine, during some former 

 suspension of eruption on the eastern flank of the volcano, that 

 ravines like the Cava Grande may have been gradually excavated in 

 the wide space separating the two hills of Calanna and of Caliato." 



In order to test the value of the hypothesis, Sir Charles explored 

 from their lower to their upper terminations the two principal valleys 

 of aqueous erosion, which slope upwards from the foot of the cone to 

 the soiithern margin of the Caldera. Those who are conversant mth 

 Junghuhn's "Yolcanos of Java" are well aware of the nature and 



value of this test ; for they will remember that the flanks of volcanic 

 cones which are in full activity are free fi'om fiuTOWs eaten out by 

 running water ; whereas, such as have been long extinct, or are in a 

 si ate of moderate activity, exhibit a great number of ravines from 

 'M)0 to (>00 feet deep, excavated by torrents, and parted from each 



