J. W.Judd—On Volcanos. 247 



Concerning the conditions under which this green tuff of 

 Epomeo was formed, we are fortunately not left in any doubt. 

 It consists entirely, as we have seen, of puniiceous fragments, 

 mingled with broken crystals of sanidine and numerous plates of 

 black mica ; these being the most common of the minerals included 

 in the ordinary trachytes of the district. The mass is often found to 

 contain, moreover, volcanic-bombs, and the proof of the tuffs having 

 been the result of the ordinary explosive action of volcanos is, 

 therefore, most complete. But mingled with these tuffs are found 

 very numerous marine shells, specimens of which I collected up to 

 a height of 1846 feet on the slopes of Epomeo, and they have been 

 recorded as occurring even at still greater elevations. It would seem 

 clear, therefore, that the tuffs must have been accumulated beneath 

 the sea-level, but at such moderate depths as not to prevent the 

 ordinary explosive action, and that disengagement of imprisoned 

 vapour and gas, to which the pumiceous structure is evidently due, 

 readily taking place. In opposition to the view put forward by 

 some geologists, — namely, that lava when poured forth under water 

 gives rise to a totally different series of products from those formed by 

 subaerial volcanic action, — I may point to the fact that these un- 

 doubtedly marine tuffs of Epomeo, abounding in shells, offer no 

 essential points of difference from the tuffs of Bagno Secco in 

 Lipari before described, or those of Somma, both of which, as we 

 have seen, contain numerous leaves and other remains of terrestrial 

 plants, and were clearly of subaerial origin. 



But in the case of the tuffs of Epomeo we have another interest- 

 ing proof of its submarine mode of origin. The tuffs are sometimes 

 interstratified with "marls," "clays," and white calcareous rocks 

 of a chalk-like aspect. The interesting analyses of these, however, 

 by Euchs, show that they are all formed from the volcanic tuffs 

 by ordinary aqueous erosion, aided to some extent by the passage 

 through the mass of gases and vapours, and the ordinary action 

 of organic beings living on the sea-bottom, especially of the mollusca, 

 in separating the carbonate of lime. In illustration of this statement, 

 we may quote the following analyses : — 





(a) 



(*) 



(o) 



(d) 



Silica 



. 59-88 



58-31 



46-28 



57-20 



Alumina 



. 17-28 



19-79 



12-71 



15-71 



Ferric Oxide 



. 5-06 



2-86 



4-46 



5-51 



Ferrous Oxide 



. 2-30 



2-11 



2-14 



2-64 



Lime 



. 1-69 



0-70 



11-27 



1-16 



Magnesia 



. 0-80 



0-81 



2-17 



2-68 



Manganese 



trace 



— 



— 



— 



Potash 



. 6-43 



6-29 



2-58 



3-19 



Soda 



. 2-97 



2-88 



0-82 



1-01 



Water 



3-69 



7-24 



8-67 



10-71 



Phosphoric Acid .. 



. 0-043 



— 



— 



— 



Carbonic Acid 



— 



— 



8-13 



— 



100-14 100-99 99-23 99-81 



(a) represents the composition of the so-called marl of Epomeo, 

 which is very largely dug, and both at Casamicciola and Naples, 

 to which latter place it is largely exported, used for making tiles 



