408 



(Mowna Roa, Peak of Teneriffe, Etna, Peak of 

 the Azores), furnish only modern volcanic 

 rocks. It would however, be an error to extend 

 that law to every other continent, and to admit 

 general that, in every zone, the greatest ele- 

 vations have produced tr achy tic domes ; gneis- 

 granite and mica-slate constitude, in the almost 

 insulated groupe of the Sierra Nevada of Gre- 

 nada, the Peak of Malhacen*, as they also 

 constitute in the continued chain of the Alps, 

 the Pyrenees, and probably the Himalaya ^, the 

 summits of the ridge. Perhaps these pheno- 

 mena, discordant in appearance, are effects of 

 the same cause; perhaps granite, gneiss, and 

 all the pretended primitive Neptunian mountains, 

 are owing to volcanic forces, as well as the tra- 

 chytes ; but to forces of which the action re- 

 sembles less the still burning volcanoes of our 

 days, ejecting lava, which at the moment of its 



* This peak, according to the survey of M. Clemente 

 Hoxas, is 1826 toises above the level of the sea, consequent- 

 ly 39 toises higher than the loftiest top of the Pyrenees (the 

 granitic peak of Nethou), and 83 toises lower than the^ tra- 

 chytic peak of TenerifFe. The Sierra Nevada of Grenada 

 forms a system of mountains of mica-slate, passing to gneis 

 and clay-slate, and which contains shelves of euphotide and 

 green-stone. See the excellent geognostic memoir of Don 

 Jose Rodrigues in the Ann, de Chimie, Tom: xx, p. £8. 



f If we may judge from the specimens of rocks collected 

 in the necks and passages of the Himalaya, or rolled down by 

 the. torrents. 



