426 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



Carboniferous in tliis region. A section, starting on tlie well-determined 

 Carboniferous limestones and carried along a soutliwest and northeast 

 line, or nearly at right angles to the strike, across Station XL ridge, is 

 shown in an accompanying plate. As this section affords what may be 

 regarded as a typical exhibition of the stratigraphic structure of a series 

 of formations which constitute an important element in the geological 

 history of the region, a detailed description is here appended. 



Section through Station XL. 



1. Gray and drab, cherty, spar-seamed Carboniferous limestone, ex- 

 posed in south flank and crest of high ridge north of Station XL ridge, 

 the southeast continuation of Station XLII ridge. 



2. Eeddish-buff sandstone, imperfectly exposed in south side of saddle. 



3. Gray limestone ledge. 



4. Very hard, flinty, gray sandstone, almost a quartzite. Dip 40°, 



s. 450 W. 



5. Light gray, slightly siliceous limestone, with chert bands. 



6. Hard reddish buff-gray sandstone. 



7. Gray siliceous limestone. 



8. Eeddish buff-gray sandstone, with dark flinty fragments and hard 

 gray siliceous layers. 



9. Dark chocolate-colored and rusty indurated deposits, obscurely 

 exposed in shallow saddle. 



10. Gray, cherty limestone, containing a large BellerojyhoTij and Den- 

 talium f 



11. Hard reddish-buff sandstone. 



12. Drab limestone. 



13. Very hard fragmentary light-buff sandstone. 



14. Very hard grayish sandstone. 



15. Hard rusty-brown laminated sandstone. 

 IQa. Dark blue shales and indurated layers. 



16&. Eeddish shales and rusty-gray indurated layers. 



17. Dark drab, thin-bedded limestone, with Lingula, small Pleuro- 

 horus f 



18. Eusty and gray, fine laminated, indurated argillo-arenaceous de- 

 posits. 



19. Eeddish shales and indurated layers, exposed in saddle and ravine 

 north of Station XL. 



20. Tough gray sandstone, dark brown stained on exposed surfaces, 

 with obscure indeterminate Lamelli branch. Dip 44°, S. 50° W. 



21. Gray and rusty indurated layers. 



22. Hard, gray, rusty-buff weathered sandstone. 



23. Gray limestone, thickness of 10 feet exposed. 

 24a. Drab indurated arenaceous shales. 



246. Eed shales. 



24c. Deep red arenaceous shales and indurated layers forming a prom- 

 inent belt of brilliant red exposures inthe north slope of the mountain. 



25. Hard, pale red or i)ink, sandstone, 75 feet, more or less. 



2Q. Eeddish shales. 



27. Grayish or dark drab, in places buff-mottled, spar-seamed, frag- 

 mentary limestone, forming a heavy ledge, 40 feet or more in thickness, 

 in crest of Station XL ridge ; dip 40°, S. 50° W. This ledge contains 

 a few imperfectly preserved fossils, among which are recognized crinoidal 

 fragments which may prove to be Fentacrinites, a largish smooth Lamelli 



