1859.] SCEOPE CONES AND CRATERS. 529 



though not always, to have been erupted in a less fluid or more pasty 

 and viscous con(fition than the augitic lavas, and on that account to 

 have accumulated in greater bulk, and occasionally in the shape of 

 lumpy excrescences over or near the orifice from which they issued. 

 The massive trachytic beds and hummocks of the Mont Dore and 

 Cantal are striking examples of this tendency ; and still better, 

 perhaps, the trachytic domes or bell-shaped hills of the chain of 

 Puys near Clermont. In the latter instance it is well worth re- 

 marking that each of them, to the number of five, rises either close 

 to or actually from the crater of an acknowledged cone of eruption 

 composed of mantling beds of ejected scoriae (see figs. 13 and 16). 

 Now, had not the composition of these cones presented such incon- 

 testable proofs of their eruptive origin — had anything in their struc- 

 ture offered the smallest excuse for attributing their formation to 

 upheaval — we should undoubtedly have had them exhibited by the 

 upheavalists as conclusive examples of craters of elevation, the 

 surrounding beds being supposed to have been tilted up by the pro- 

 trusion en masse of the trachytic domes that rise from their centres. 

 But that being inadmissible ; since, on the contrary, we have in them 

 undeniable examples of bulky domes of trachytic lava, whose emission 

 was in each case evidently accompanied or succeeded by explosive 

 eruptions, the ejection of scoriae, and the formation of cones and craters 

 from their accumulation, is it not most reasonable to believe that 

 in the other instances of Astroni, Camaldoli, Eocca Monfina, &c., the 

 same order of events occurred, and that these cones and craters, as 

 well as the trachytic lavas they contain, are also of the ordinary erup- 

 tive character ? Indeed I can assert from my own observation that 

 this is so as respects some of them. The Pipemo of Pianura in the 

 crater of Camaldoli is proved, by the elongated shape of its vesicular 

 cavities and dark concretionary patches, to have flowed as a lava. 

 The trachyte of Olibano has evidently descended as a lava the outer 

 slope of the cone of the Solfatara, on which it may be seen to rest at 

 a high angle in a massive bed reaching from the upper edge of the 

 crater to the sea. In Ischia there are several trachytic lava-streams 

 or hummocks which have been poiu'ed out of the craters of very 

 recent-looking cones of scoriae and pumice. In Bocca Monfina, 

 trachytic lavas exactly similar to that of the central boss are seen 

 to issue from three or four unquestionable parasitic crater- cones 

 on the outside of the principal cone. 



M. de Humboldt speaks uniformly of the great dome-shaped tra- 

 chytic mountains of South America as mere crusts that have swelled 

 at once like enormous hollow blisters, sometimes having burst at the 

 sumimit, and in this case possessing a central crater, in other in- 

 stances remaining "unopened*." But, as the greater number of 

 these mountains are in part composed of fragmentary pumice, there 

 has evidently in their instance been a great disengagement of elastic 

 vapours within the mass of lava, and eruptive explosions accompany- 

 ing their protrusion. ISTor is there any feature in the appearance or 

 structure of any of them, as described by M. de Humboldt himself, 



* Kosmos. p. 224. 



