0^'LAHOMA ACADEMY OF SCIENCE 



111 



cent of olivine phenocrysts, which were the largest in the rock, 

 showed the most perfect outlines. They were as much as 1.3 mm. 

 long and ybout .75mm. wide a'thoitgh most of the crystal'' were 

 much smaller. They were also the only minerals showing marked 

 decomposition to iron ores, hematites etc. fhis decompo 'ton was 

 only initial however, as very little serpentine was noted. The olivine 

 had magnetite inclusions. The microscopic examination was not 

 particularly satisfactory in identifying closely either the pyroxene 

 or the plagio^lase, owing to the extremely tine texture but it did 

 dei'initely place the rock as an olivine diabase. 



Fig. 6. Photcm'ct'^ graph of Black mesa basalt. Ordinary 

 light X 80. C. W. Honess. 



In the ac"ompanying photomicrographs of the Black Mesa basalt 

 ty C. W. Honess, Chief Geologist for the Oklahoma Geological 



Survey, the long slender white minerals arc unv, i^i j^-;>« tVip 



ro-anded white areas are the vesicles, the light shaded areas are 

 the pyroxenes. The other minerals are almost indistinguishable. 



The above results of rhe microscopic examination in thin sec- 



