SECTIONS m THE SEVIEE PLATEAU. 



241 



Section IV. — Monroe Amphitheater. 



Beginning near the central part of the upper verge of inner amphi- 

 theater; altitude, about 9,400 feet and descending west. 



Feet. 



1. Granitoid trachyte 80 



2. Dolerite, brownish gray, much weathered on the surface, much shattered 



and splintered and falling apart in slabs and tiles, probably numerous 



layers, not distinctly separable IGO 



3. Granitoid trachyte, rather dark gray, slightly homblendic, and somewhat 



fine grained 35 



4. Granitoid trachyte, finer than above and rather lighter in color 30 



5. Granitoid trachyte, like No. 3 50 



6. Granitoid trachyte, a little darker and coarser than the preceding G5 



7. Dolerite 15 



8. Argilloid trachyte, numerous sheets very massive aud not distinctly sepa- 



rated 420 



9. Dolerite 50 



10. Argilloid trachyte 50 



11. Argilloid trachyte GO 



12. Argilloid trachyte . 55 



13. Trachytic conglomerate 140 



14. Granitoid trachyte, dark colored, coarse grain, very hard and compact, and 



iu very massive layers 180 



15. Dolerite or augitic andesite (?) 10^ 



IG. Hornblendic trachyte, dark and rather flue grained 110 



17. Hornblendic trachyte 40 



18. Hornblendi') trachyte 50 



19. Dark granitoid trachyte 50 



20. Hornblendic trachyte - - 95 



21. Granitoid trachyte, light brown 33 



22. Hornblendic trachyte, dark, coarse grained. This and the preceding num- 



bers below 15 probably consist of several layers each, not well separated. 75 



23. Augitic andesite in many layers, hard, compact, fine grained, and all very 



similar in appearance 2G0 



24. Conglomerate, containing fragments of hornblendic trachyte and hornblen- 



dic andesite CO 



25. Hornblendic trachyte, numerous layers (?)350 



26. Homblendic andesite, no g<Jod estimate possible, but not less than 200 



16 H p 



