94 BUNSEN ON THE FORMATION OF 



which approximates remarkably near to the corresponding rela- 

 tion in palagonite, 3 : 1-95. The palagonite rock of Laugar- 

 vatnshellir possesses almost exactly the same composition, cal- 

 culated for anhydrous substance, as this rock, which is so totally 

 different from it in all its characters : — 



112. 



Silica 50-71 



Alumina 13'55 



Protoxide of iron , . 15*44 



Lime 10*75 



Magnesia .... 7*98 



Soda 0-76 



Potash 0*81 



100-00 



If this carbonate of lime, amounting to more than 8 per cent., 

 had been deposited by percolating calcareous water, and did not 

 result from the penetration of carbonic acid into the moist rock, 

 it would be inconceivable why the per-centage of lime in the dis- 

 seminated calcareous spar should give almost exactly the com- 

 position of the original rock ; and further, why such an enor- 

 mous process of extraction should have failed to exercise any 

 influence upon the so readily decomposable alkalies ; and finally, 

 how such a deposition of lime could have taken place at all in 

 the compact rock, entirely destitute of cavities. Without at- 

 tempting here to follow up these relations more closely, it may 

 suffice to bring forward a few more examples of these fumarole 

 actions which are frequently met with in Iceland, without any 

 connexion with the course of the spring strata, and com- 

 mencing from the plutonic dykes spread out into the sur- 

 rounding rocks. 



At the spot where, on the road from Hruni to Storinupr, the 

 Laxa is first met with, there rises on the south-eastern bank of 

 this river the trachytic precipice Arnarhnipa, which is traversed 

 by a pyroxenic dyke, whose edges are converted by fumarole 

 action into a soft lavender -blue clay containing pyrites and 

 carbonate of lime, and possessing the following composi- 

 tion • — 



