458 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



of change. In Putnam county, the sandstone is very thin, with an 

 unusual thickness of shale above and below it, the greater part of 

 the mass having been replaced with shale ; in Warren county, pebbles 

 seem to be wanting and the rock is merely a cross-bedded sandstone. 

 Where the mass passes under cover on the east side of this area, it 

 is much less coarse than along the outcrop line.*" 



On the eastern side of the coal area in Tennessee, the Bonair is 

 largely pebble rock near the Alabama line, but at 20 miles north, it 

 is sandstone, 65 to 75 feet thick, and this is its character for several 

 miles. But, at 32 miles from the Alabama line, it is a mass of " con- 

 glomerate and massive sandstone," a condition prevailing northward 

 at all exposures for about 30 miles ; but, thence until near the Vir- 

 ginia line, the sections show only sandstone with some shale, there 

 being apparently no pebble rock. The outcrop on this side trends 

 considerably east of north, so that, near the \^irginia line, one is 75 

 miles away from the western outcrop ; yet the rock is without pebbles, 

 whereas on the western side, in the Ohio basin, it is coarse and pebbly. 

 The probable equivalent in southwest Virginia is for the most part 

 loosely cemented sandstone with shale, changing to shaly sandstone 

 toward the west but becoming a great sandstone with some pebbles at 

 a few miles farther along the extreme easterly outcrop. Beyond 

 New River in West Virginia, the Bonair horizon has been recog- 

 nized for about 40 miles ; ordinarily the rock is merely a sandstone, 

 but, toward the northern termination, the outcrop is carried eastward 

 and, at the extreme exposure, one finds the rock very coarse with 

 quartz pebbles abundant and at times with diameter of 2 inches. 

 Westwardly it decreases rapidly and within a few miles thins out 

 against the slope of Alleghania.*^ 



Returning to the south and going southeastwardly in Alabama, 

 one finds striking changes in the Bonair. In that state are several 

 troughs, separated by narrow intervals and lying southeast from the 

 continuous area, followed thus far, while that area extends unbroken 



^This summary is based on observations by J. M. Safford, C. W. Hayes, 

 M. R. Campbell, recorded in " Carboniferous of the Appalachian Basin," 

 Bull. Geol. Soc. Amer., Vol. 15, 1904, PP. 1 14-126, 136-146. 



^ For the observations of Campbell, Hayes, F. H. Bradley, Safford, I. C. 

 White and Stevenson, see Bull. Geol. Soc. Amer., as above, pp. 136-190. 



