120 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



line. The Lookout sandstone of Hayes, having the Main (Bonair) con- 

 glomerate as its upper bed, forms the plateau, with detached areas of 

 Walden sandstone in the several counties. The Lookout, inclusive of the 

 Bonair, decreases from 510 feet at Sequatchie valley to 120 feet at the 

 western outcrop. Mr Hayes finds the Walden 550 feet in eastern 

 Grundy, 475 in eastern Marion, and only 300 feet in southern Grundy. 

 These figures refer not to the full thickness, but only to that of the por- 

 tion remaining. Professor Safford gives a detailed section near Tracy 

 City, in southern Grundy and northern Marion, as follows : 



Feet. Inches. Feet. Inches 



1. Conglomerate [Rockcastle] 50 



2. Coal bed. 



3. Shale.. .'. 23 



4. Coal bed 6 



5. Shale 26 



6. Sandstone 86 



7. Sandy shale 45 



8. Coal bed [main Sewa nee]. , 3 to 7 



9. Shale 33 



10. Coal bed 1 



1 1. Shale and sandstone. 17 



12. Conglomerate [Bonair] 70 



13. Coal bed 1 to 6 



14. Shale 10 



15. Cliff sandstone [Etna] 65 



16. Coal bed [Etna] 1 6 to 6 



17. Shale 30 



18. Hard sandstone 78 o 



19. Coal bed 1 to 3 



20. Hard sandstone 20 



21. Shale to mountain limestone 20 



The average thickness of the Upper Measures is given as 240 feet, and 

 that of the Lower Measures as 228 feet, not including the conglomerates. 

 The sandstone of White county below the Rockcastle has doubled in 

 thickness, and the Sewanee coal bed is at a greater distance above the 

 Bonair, though less than in central Bledsoe, where it is possible some of 

 the interval may be accounted for by uncertainty respecting the top of 

 the Bonair. The average interval in these southern counties is not far 

 from 50 feet. The Cliff sandstone, extending northward apparently no 

 farther than White county, increases in importance south wardly and is 

 a marked feature in much of Alabama ; but the interval between it and 

 the Bonair is variable; sometimes the two deposits are in contact, while 

 at others they are separated by 150 feet. In northern Grundy they seem 

 to be in contact, for there Professor Safford 's section is 



