92 BUNSEN ON THE FORMATION OF 



a full explanation of the nature of the metamorphosis which has 

 taken place. 



108. 



Silica 46-47 



Alumina .... 14*71 



Protoxide of iron . . 14*29 



Lime 8-04 



Magnesia .... 4*98 



Soda 1-53 



Potash 0*87 



Carbonate of lime . 5*35 



Pyrites 1*04 



Water 3*58 



Gypsum trace 



100-86 



We here observe the remarkable fact, that when the per-centage 



of lime and protoxide of iron, which has suffered from the me- 



tamorphic action, is again added to the original silicate, we 



obtain almost exactly the composition of the normal pyroxenic 



substance, thus : — 



109. 



Silica 49-17 



Alumina .... 15-57 ^ ^i-^'i 



} 



Protoxide of iron . 15-78 



Lime 11*68 



Magnesia .... 5*27 



Soda 1-62 



Potash 0*92 



100*00 



The composition, which, as in the normal pyroxenic substance, 

 corresponds to the relation between the quantities of oxygen in 

 the acid and bases of 3 : 1*936, proves that the change which 

 has taken place in the rock cannot have been connected with 

 any sensible extraction, and that consequently it was not cur- 

 rents of water, but the gases and vapours dissolved in the water 

 which attacked and caused the metamorphism of the rock. The 

 remarkable trachyte dyke at the south-eastern foot of the Esja- 

 mountains, whose interfusion with the adjoining pyroxenic rock I 



