^_To face page 72. 



VIIL— i. 



DIORITE, ., 12, 

 WITH VEIN OF GRANITITE, 

 MUTOSSE, CUYUNI RIVER. 



Photo by J. Williams 



HORNBLENDE SYENITE, x 12, 

 PIGEON ISLAND, ESSEQUIBO RIVER. 



Fhofo hy J. TTilUan 



