Ch. XXXI.] NEWER PLIOCENE VOLCANIC ROCKS. 065 



CHAPTER XXXI. 



ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS, Continued. 



Volcanic rocks of the Newer Pliocene period — Val di Noto — Sicilian dikes — Region 

 of Olot in Catalonia — Volcanic rocks of the Older Pliocene period — Tuscany — 

 Rome — Volcanic region of Olot in Catalonia — Cones and lava-currents — Ravines 

 and ancient gravel-beds — Jets of air called Bufadors — Age of the Catalonian 

 volcanoes — Upper Miocene period — Volcanic archipelagoes of Madeira, the Ca- 

 naries, and the Azores — Lower Miocene period — Brown-coal of the Eifel and 

 contemporaneous trachytic breccias — Age of the brown-coal — Peculiar characters 

 of the volcanoes of the upper and lower Eifel — Lake Craters — Trass — Hungarian 

 volcanoes. 



VOLCANIC ROCKS OF THE NEWER PLIOCENE PERIOD. 



Vol di Noto. — I have already alluded (see p. 192) to the igneous 

 rocks which are associated with a great marine formation of lime- 

 stone, sand, and marl in the southern part of Sicily, as at Vizzini 

 and other places. In this formation, which was shown to belong to 

 the Newer Pliocene period, large beds of oysters and corals repose 

 upon lava, and are unaltered at the point of contact. In other places 

 we find dikes of igneous rock intersecting the fossiliferous beds, and 

 converting the clays into siliceous schist, the laminae being contorted 

 and shivered into innumerable fragments at the junction, as near the 

 town of Vizzini. 



The volcanic formations of the Yal di Noto usually consist of the 

 most ordinary variety of basalt, with or without olivine. The rock 

 is sometimes compact, often very vesicular. The vesicles are occa- 

 sionally empty, both in dikes and currents, and are in some localities 

 filled with calcareous spar, arragonite, and -zeolites. The structure 

 is, in some places, spheroidal ; in others, though rarely, columnar. I 

 found dikes of amygdaloid, wacke, and prismatic basalt, intersecting 

 the limestone at the bottom of the hollow called Gozzo degli Martiri, 

 below Melilli. 



Dikes in Sicily. — Dikes of vesicular and amygdaloidal lava are also 

 seen traversing marine tuff or peperino, west of Palagonia, some of 

 the pores of the lava being empty, while others are filled with carbon- 

 ate of lime. In such cases we may suppose the peperino to have 

 resulted from showers of volcanic sand and scoria?, together with 

 fragments of limestone, thrown out by a submarine explosion, similar 

 to that which gave rise to Graham Island in 1831. "When the mass 



