1912] STEVENSON— THE FORMATION OF COAL BEDS. 459 



into the Warrior coal field. Raccoon mountain, a prong from the 

 continuous area, shows on its westerly side the Bonair sandstone, 

 30 to 50 feet thick and in great part pebbly ; but on the easterly side 

 the thickness is 75 to 80 feet and the rock is almost wholly pebbles. 

 On Blount mountain, the southern prolongation of the east side of 

 Raccoon, the mass thickens southwardly along the strike to 100 and 

 finally, as estimated, to 500 feet. It is not pebbly throughout, but 

 in portions where conglomerate prevails, the pebbles are not cemented 

 firmly. In the small Lookout area, the Bonair is 50 to 60 feet thick 

 and very coarse near the Georgia line, but at 10 miles southwardly it 

 is a moderately coarse sandstone. The Cahaba basin is only a short 

 distance southeast from the strike-line of the Lookout, but the 

 interval sufficed for great change and the Bonair horizon is marked 

 by more than 600 feet of conglomerate, sandstone and gritty shales; 

 while in the Coosa field, only a few miles farther southeast, the rock 

 is coarse conglomerate about 500 feet thick. The Lookout area, at 

 the Tennessee line, is barely 30 miles from the present border of 

 Archaean and the Coosa area is several miles nearer. The latter is 

 not more than 30 miles from Raccoon mountain in direction of dip. 

 The rock is coarsest in Coosa, less so in Cahaba. less in Blount and 

 still less in Raccoon ; in the Warrior basin beyond, one finds the 

 Bonair persistent almost to the western boundary of Alabama, but 

 losing its coarseness and at length replaced more or less with shale.** 

 Certain features of the Bonair should be emphasized. Where 

 the western border of its area is approached in Alabama and at a 

 few localities in central and northern Tennessee, the rock is less 

 thick, with few pebbles, a more or less cross-bedded sandstone, at 

 times replaced in part with shale. Along the western outcrop in 

 Tennessee, aside from the extreme western localities, the rock con- 

 sists, in considerable spaces, very largely of pebbles, while in other 

 and intervening considerable spaces, it is merely a sandstone with 

 layers of pebbly rock varying in number and thickness in different 

 localities. And this condition exists where the Bonair passes under 

 cover toward the east, as also where the equivalent area is cut by 



" For the observations by H. McCalley, A. M. Gibson, Safford, Hayes 

 and J. Squire, see as above, pp. 126-136. 



