THE VOLCANIC ROCKS OF ICELAND. 



55 



Silica . . . . 

 Alumina . . . 

 Protoxide of iron 

 Lime . . 

 Magnesia . 

 Potash . . 

 Soda . . 

 Water . . 

 Foreign residue 



Iceland, Naefrholt near Hecla, 



Oxygen found. 

 17-39 



8-47 



5-03 



Oxygen calculated. 

 17*65 



8-83 



4-41 



100-42 



Iceland Tuff, containing Fossils, from Folsvogr, 



99-27 



Iceland Detritus from the Lava near Hruni, 



10000 



