278 bulletin: museum of comparative zoology. 



41a bis. Diabase or coarse basalt. This probably Culebra 



Summit^ 41a. 

 41.1. White and red banded rock. Isotropic in slide. Sili- 



cified or cherty. 

 41.2 and 41.3. Porphyrite. 



(43) Beach drift at Market Front, Panama. A fine grained green- 

 ish diabase porphyrite. 



(44) Culebra, Isthmus of Panama. Dense greenish eruptive rock 

 diorite porphyrite. 



(46) Pebbles from Cut 1 at Culebra section. (See page 195.) 



1. Chert. 



2. Cherty tuff (with feldspar fragments). 



3. Silicified tuff with large feldspar fragments. 



4. Fine grained black shale siliceous with feldspar fragments. 



(47) Gravels at junction of the River Chagres with the Obispo, Isth- 

 mus of Panama ; brought down by river from unexplored interior. 



1. Granite. 



2. Green rock containing granite fragments ; fine grained augite 



porphyrite. 



3. Granite. 



4. Fine grained quartz diorite. 



5. Decomposed porphyrite. 



6. Granite. 



7. Basalt. 



8. Basalt. 



9. Very much altered quartz porphyry or rhyolite. 



10. Quartz diorite porphyrite. 



11. Augite andesite. 



12. Epidotized diabase-porphyrite. 



13. Black cherty siliceous shale. 



14. Basalt. 



15. Greenish porphyrite. 



1G. Dark gray augite porphyrite. 



17. Quartz porphyrite. (See 27.) 



18. Glassy hypersthene-andesite. 



19. Decomposed quartz-porphyry. 



20. Probably chert. 



21. Granite. 



22. White granophyric quartz-porphyry. 



23. Granite. 



