ORIGIN OF ERUPTIVE AND PRIMARY ROCKS. 311 



6. Trachyte from Krabla. 

 1. Obsidian from Krabla. 



1. 2. 3. 4. 5. 6. 7. 



Silica 75.91 77.92 75.29 78.95 76.42 76.38 75.77. 



Alumina 11.49 12.01 12.94 10.22 9.57 11.53 10.29. 



Ferrous oxide 2.13 1.32 2.60 2.91 5.10 3.59 3.85. 



Lime 1.56 0.76 1.01 1.84 1.53 1.76 1.82. 



Magnesia 0.76 0.13 0.03 0.14 0.20 0.40 0.25. 



Soda 2.51 4.59 2.71 4.18 5.24 4.46 5 56. 



Potash 5.64 3.27 5.42 1.76 1.94 1.88 2.46. 



100,00 100.00 100.00 100.00 100.00 100.00 100.00 



The mean of these analyses is : 



Silica 76.662 



Alumina. 1 1.15o\ 



Ferrous oxide 3.071 ) 



Lime 1.469 ( 23.338 



Magnesia 0.274 ( 



Soda 4.178] 



Potash , 3.196/ 



100.00. 



This Bunsen assumes to be the composition of the normal 

 trachytic mass, which occupies one of the reservoirs of his theory. 

 The second series of analyses comprised those of the following 

 rocks : 



1. Trap rock from Esiaberg„ 



2. Trap from Vidoe. 



3. Light fine grained basaltic rock from Hagafgell on the right 



bank of the Thiorsa. 



4. Basaltic rock from Skardsfjall. 



5. Lava from an old stream of Hecla. 



6. Rock from the precipice of Almannagjo near the lake of 



Thingvalla. 



1. 2. 3. 4. 5. 6. 



Silica .....50.05 47.48 49.17 47.69 49.37 47.07. 



Alumina 18.78 13.75 14.89 11.50 16.81 12.96. 



Ferrous oxide 11.69 17.47 15.20 19.43 11.85 16.65. 



Lime 11.66 11.34 11.67 12.25 13.01 11.27. 



Magnesia 5.20 6.47 6.82 5 83 7.52 9.50. 



Soda .... 2.24 2.89 0.58 2.82 1.24 1.97. 



Potash 0.38 0.60 1.67 0.48 0.20 0.58. 



100.00 100.00 100.00 100.00 100.00 100.00. 



