THE VOLCANIC ROCKS OF ICELAND. 43 



The calculated relation of trachyte and pyroxenic masses in 

 this rock is 1*0 to 5-117. 



Experiment and calculation gave for a trap (clinkstone ?) from 

 EskiQordhr, analysed by Damour, 



34. 

 Found. Calculated. 



Silica 66-12 66*12 



Alumina and protoxide of iron , 24*05 20*20 



Lime 3*24 5*34 



Magnesia 0*46 2*76 



Potash 1*29 2*24 



Soda 4*84 3*34 



100*00 100*00 



This rock represents a mixture of 1*0 trachyte and 0*5991 

 trap mass. 



A clinkstone from Klettaberg near Kalmanstunga, in sepa- 

 rate slabs, consisted of — 



35. 

 Found. Calculated. 



Silica 73-37 73*3? 



Alumina and protoxide of iron . 17*26 16*09 



Lime 2*49 2*66 



Magnesia 1*52 1*05 



Potash 3-01 2*90 



Soda 2*35 3*93 



100*00 100*00 



The relation of the normal trachytic and pyroxenic masses is 

 in this instance 1 : 0*1325. 



A great number of other analyses of this kind, which some- 

 times showed a greater difference and sometimes a still greater 

 correspondence between the experimental and calculated results, 

 lead to the same conclusion. 



But even if these examples should leave any doubts of the 

 existence of an intimate connexion between the various unal- 

 tered rocks occurring in Iceland, such doubts must be entirely 

 removed by the evidence presented in favour of such connexion 

 by a great number of trachytic and basaltic dykes. It is here 

 very frequently possible to detect the intermixture of the extreme 

 acid and basic members, not only by means of chemical analysis, 

 but by direct observation. In one of the south-eastern valleys of 



