928 CHEMICAL COMPOSITION OF KOCKS OF THE LIZAKD DISTKICT. 



III. 



Analysis of the Carnpersack Bock (p. 902). — A very hard tough 

 variety, poor in diallage. occurring in the great dyke-like mass of 

 gabb.ro which comes down to the sea at Karak Clews. The analysis 

 therefore represents the condition of one of the more " saussu- 

 ritic v varieties of the last rock. 



Dried at 100° C. 



Ignition (chiefly water) 1-13 



Silica 49-50 



Alumina 18*75 



Oxides of iron 1*50 



Lime 20-62 



Magnesia 8*00 



Alkali (?) and loss -50 



100-00 



IV. 



The hornblende schist of the Lizard presents many varieties, 

 which, on analysis, would differ materially as to quantities. The 

 following is from a variety of high specific gravity occurring near the 

 lighthouse. About one fourth of the rock is soluble in acid. It con- 

 tains a noteworthy amount of pyrites and phosphoric acid. 



Dried at 100° C. 



Ignition (water) 1-30 



Silica 47-40 



Alumina , 19-30 



Oxides of iron 11-40 



Lime 11-80 



Magnesia 7'75 



Alkali (?) and loss 1-05 



100-00 



(For the Discussion on this paper see p. 460.) 



