X.— i. 



FINE-GRAINED DIABASE, x 40, 

 TINAMU, CUYUNl RIVER. 



Pho/o by J. If'ilHiims. 



COARSE-GRAINED DIABASE, x 30, 

 TAKWARI MOUNTAIN, ESSEQUIBO RIVER. 



Fhoto by J. IViHiams 



