Notice of Active and Extinct Volcanos. 81 



The composition of the lava That of Santa Vennera, 

 of Catania, near Etna, as as- Piedmont, west of Etna, 

 certained by Dr. Kennedy, is, 

 is, 



Silex, 51. 50.75 



18.5 



10. 



14.25 



4. 



1. 



Alumina, 



19. 



Lime, 



9.5 



Ox. Iron, 



14.5 



Soda, 



4. 



Muriatic Acid, 



1. 



100. 100. 



The author has reviewed the structure and mineralogical 

 and chemical composition of the volcanic masses, in order 

 to shew the correspondence of facts, with the theoretical 

 views which he has adopted, and it must be allowed, that he 

 has so far made out his case, that there appears to be nothing 

 connected with volcanos, which militates against the sup- 

 position of their origin from metalloids, acted on by water. 



There is good evidence that " volcanos have univer- 

 sally broken out amongst the older formations, or those most 

 near to the nucleus, whatever it may be, of the globe." The 

 lavas themselves appear to be the materials of primitive 

 rocks, altered by fire, and the accidentally imbedded frag- 

 ments are portions of primitive rocks. It seems to be irre- 

 sistibly inferred, that the seat of volcanic action is deep, be- 

 cause the immense masses ejected from such mountains as 

 Vesuvius and Etna do not exhaust them — because the mate- 

 rials are raised to a vast height, as at Teneriffe and Cotopaxi, 

 and because the mountains are not shattered by the tremen- 

 dous explosions, which would blow up any superficial strata 

 into the air. 



" Let us suppose, (says our author,) that the nucleus of the earth 

 at a depth of three or four miles, either consists of, or contains as a 

 constituent part, combinations of the alkaline and earthy metal- 

 loids, as well as of iron and the more common metals, with sulphur 

 and possibly with carbon. These sulphurets are gradually undergo- 

 ing decomposition, wherever they come into contact with air and 

 water, but, defended by the crust of the globe, just as a mass of 

 potassium is by a coat of its own oxide when preserved in a dry 

 place, the action goes on too slowly to produce any striking effect, 

 unless the latter of these agents be present in sufficient quantity. 

 Hence under our continents, the elastic fluids generated by this 



Vol. XIV.— No. 1. 11 f 



