42 BUNSEN ON THE FORMATION OF 



31. 

 Found. Calculated. 



Silica 73-57 73-57 



Alumina and protoxide of iron . 17*19 15-89 



Lime 1-41 2-58 



Magnesia 0-81 I'Ol 



Potash 2-19 2-92 



Soda 4-83 3-93 



10000 10-00 



The calculation requires that there should be 0-1325 pyroxenic 

 mass to 1-0 of trachyte. Another compact gray pyroxenic rock 

 from Reyjadalr Foss, a small waterfall which is formed by the 

 Nordhra near Hvammr, shows a still greater correspondence. 

 This rock was either massive or separated by columnar fissures, 

 and contained small zeolitic druses filled with green earth. 



32. 

 Found. Calculated. 



Silica 51-75 51-75 



Alumina and protoxide of iron . 28-39 28-31 



Lime 10-49 10*65 



Magnesia 5-90 6*13 



Potash 1-01 0-96 



Soda 2-46 2-20 



100-00 100-00 



The calculation requires 7*597 pyroxenic mass to 1*0 trachyte. 

 A compact blackish gray rock, with an indistinct angular frac- 

 ture in small pieces, and a conchoidal fracture in large pieces, 

 presenting a very uniform crystalline granular appearance, and 

 occurring in the neighbourhood of Kalmanstijnga, which affords 

 particularly good opportunities for the study of the mixed rocks, 



consisted of — 



33. 



Found. Calculated. 



Silica 53-08 53-08 



Alumina and protoxide of iron . 28-70 27*57 



Lime 9*92 10'16 



Magnesia 5-32 5-81 



Potash 0-61 1*06 



Soda 2-37 2-32 



100-00 100-00 



