The Petrography of the Fundamental Gneissose Complex . 51 



CUYUNI RIVEK, NEAR SUARIMA ISLAND. 



Orthoclase ... 



Albite 



Zoisite 

 Hornblende... 



Tale 



Serpentine ... 



Ilmenite 



Magnetite ... 



Calcite 



Minor constituents 



Epidioi-ite 



amphtbohte). ^ "' I Hnpk. 



100-0 



F.SSEaVIBO DISTRICT. 



E/>idiorife. 



Quartz ... 



Orthoclase 



Andesine (Ab^ An.,) ... 



Labradorite (Abo An.^)... 



Hornblende 



Magnetite 



Ilmenite... 



Calcite 



Minor constituents 



Hornblende-schist . 



The epidiorites aucl hornblende schists belong to two classes ; in the 

 first of which, represented l)y many of those of the Mazaruni-Cuyuni 

 district, the hornblende is chiefly uralitic passing to actinolite, the 

 formation of which has been accompanied by the extrusion of relatively 

 high proportions of magnetite from the original pyroxenes, whilst in 

 the second — the majorit}' of those from the North-west and the 

 Essequibo districts- — the original pyroxenes have re-crystallised as green 

 hornblende with smaller proportions of extruded magnetite. 



According to their ultimate mineralogical compositions these rocks 

 belong to the following classes : — 



Epidiorite, Issorora, North-Western district ... ... Kedabekose. 



,, Arakaka district ... ... ... ... ... „ 



„ TJrinambo, North-Western district Auvergnose. 



Hornblcnde-?chist, Maburima, North- Western district ... „ 



Epidiorite. Mazaruni Kiver ... ... ... ... ... Camptonose. 



Amphibolite, Mazaruni-Puruni district .. .. ... Anvergnose. 



