48 



Till' Geology of the, Gold Fields of British Guiana. 



THE CHEMICAL AND MINEHALOtJICAI. COMPOSITIONS OF THE EPIDIOEITES, 

 AMPHIBOLITE8, AND HORNBLENDE-SCHISTS. 



The chemical compositions of these rocks are as follows : — 



NORTH-WESTEKN DISTRICT. 



Silica 



Alumina 



Iron peroxide 



Iron protoxide 



Magnesium oxide ... 



Calcium oxide 



Sodium oxide 



Potassium oxide 



Water 



Carbonic anhydride 



Titanium oxide 



Phosphoric anhydride 



Iron sulphide 



Manganese oxide . . . 



Ep'nhuritt 



Issorora Urinambo 



Hill, [ Arakaka i HUI, 



Aruka i District. Barama 



River. River. 



49-06 



18-87 



1-89 



4-49 



10-95 



11-70 



0-97 



0-06 



0-43 



0-88 



trace. 



0-02 



0-34 



99-66 



49-46 



16-77 

 1-98 

 6-57 

 9-33 



11-17 

 1-55 

 0-04 

 2-02 

 0-27 

 0-79 



trace. 



trace. 



trace. 



99-95 



52-78 

 13-66 

 2-40 

 8-64 

 7-95 

 9-52 

 2-34 

 0-20 

 1-89 



0-23 



0-02 

 0-11 



Ilorxblcndf- 

 schist. 



Maburima 



Hill, 



Aruka 



River. 



99-74 



50-28 



15-72 

 •2-26 



10-35 

 9-06 



10-10 

 1-79 

 0-16 

 0-40 



0-07 



0-02 

 trace. 



100-21 



