452 Bendrat — Notes on Region about Caicara, Venezuela. 



with dentated margins; that am pinhole of hronze hrown to 

 dark-green color occurs in irregular patches ; that tourmaline 

 is occasionally met with in radiated aggregates : that garnets 

 also occur and some magnetite. These facts point to the pneu- 

 matolytic origin of these veins. The quartz has wavy extinc- 

 tion, which goes to show that after the vein had been formed, 

 together with the enclosing wall rock — in this case the granite, 

 it was subjected to dynamic stress. 



In concluding the writer wishes to remark, that it would be 

 of great interest to ascertain the geologic and petrographic 

 nature of other outliers in those waste plains that approach 

 the Orinoco from the south and east, as well as the character 

 of the rocks that make up the mass of the Guiana mountain 

 system, in order to bring out facts that would bear on the rela- 

 tions of those cerros to this area, which is probably Archean. 



