62 



Tha Geolo(jy of the Gold Fields of British Guiana. 



The following are the specific gravities of the rocks of the group : — 



Assays made upon representative samples of the rocks of this series, 

 botli of the massive and of the schistose varieties, showed that all 

 contain traces of gold and of silver, the avei'age yield l)eing at the rate 

 of 4 grains of gold and 4 grains of silver per ton of the rock. 



