ALABAMA 133 



The variable bed, represented by numbers 2, 3, and 4, is at the Sewa- 

 nee horizon, and number 6 is at the Jackson horizon of southern Ten- 

 nessee ; both beds seem to be persistent to the southern end of the field, 

 and the Sewanee is mined to some extent for use in Gadsden. The 

 Cashie coal bed is important near Fort Payne of De Kalb county, but in 

 Cherokee and Etowah it rarely exceeds 1 foot. It often underlies the 

 Bonair directly and sometimes it is distributed irregularly through the 

 bottom layers of that deposit. In like manner the Etna coal bed often 

 occurs as strings or pockets in the Etna sandstone and it is rarely of any 

 value. The Dade coal varies greatly, but sometimes, as at the Eureka 

 mines in De Kalb, is thick enough to be mined, but all of the beds tend 

 to become thinner toward the southern end of the field. 



The Bonair is very coarse near the Georgia line ; it becomes less coarse 

 southward, and within 8 or 10 miles is merely a coarse sandstone, about 

 60 feet thick. The Etna is not conglomerate ; usually is a more or less 

 cross-bedded sandstone, much of it massive. In De Kalb it is about 60 

 feet ; in Cherokee, from 75 to 100 feet, and in Etowah about 75 feet. 

 The interval between Bonair and Etna varies from 15 to 60 feet, and the 

 total thickness from the top of the former to the bottom of the latter is 

 somewhat more than 200 feet, approximately the thickness assigned by 

 Professor Spencer to his Upper Conglomerate at the north end of the field.* 



The Cahaba coal field, embracing portions of Saint Clair, Jefferson, 

 Shelby, and Tuscaloosa counties, was studied by Mr Squire wholly with 

 a view to determine economic values, so that the details of beds, aside 

 from coals, are scanty. The diagrammatic sections on the map reveal the 

 presence of very little shale, the rocks being sandstone, gritty slate, and 

 conglomerate. The topmost 500 feet are almost wholly conglomerate. 

 The aggregate thickness assigned by Mr Squire is 5,525 feet. The con- 

 ditions observed in Blount mountain are clearly only a transition from 

 those in Raccoon to those in Cahaba, as well as to those in Coosa. The 

 Millstone Grit group is about 1,700 feet thick, and consists mostly of 

 pebbly rocks and gritty slates. There are evidently three great beds of 

 conglomerate separated by gritty slates, with several thin coal beds, only 

 two of which appear to be persistent. One of these underlies what may 

 be taken as the Etna conglomerate, and is at about 250 feet above the 

 Lower Carboniferous limestone, the interval being filled with rocks less 

 coarse than the overlying conglomerate. On top of the massive Etna, 

 about 300 feet thick, one finds gritty slates extending to the second great 

 conglomerate, which with the slates is about 650 feet. The upper divis- 



* H. McCalley : Coal Measures of Plateau Region, pp. 84, 87, 88, 89, 91, 94-97, 105. 

 XVIII— Bull. Geol. Soc. Am., Vol. 15, 1903 



