276 D. WHITE — DEPOSITION OP APPALACHIAN POTTSVILLE 



ments are thicker, the contact of the Coal Measures with the Mississip- 

 pian is sharper, with the immediate introduction of massive conglomer- 

 ates, while the interval below the Raleigh is much lessened, if I am right 

 in regarding the Rockwood coal as overlying the Bon Air conglomerate. 

 I am therefore disposed to believe that between the region of the Taze- 

 well, Virginia, quadrangle and central Alabama the present eastern 

 margin of the coal field falls slightly west of the axis of the trough. 



If we have to do with a narrow basin rather than a series of small 

 basins along the axis, it is probable that the early Pottsville trough 

 swept southwestward with a gentle curve from the Southern Anthracite 

 field toward the border of the Great Flat Top region south of New river. 

 This is indicated by the very rapid steepening of the floor of the basin 

 along the margin of the coal field in eastern West Virginia.* 



Southward from the Great Flat Top region the axis is assumed to have 

 lain east of the present coal field, though it is possibly reached in the 

 Coosa and Cahaba fields, where, notwithstanding the rapid westward 

 thinning of the series, it would seem that a great thickness of the Lower 

 Pottsville must be present, since even in the heart of the Warrior basin 

 a depth perhaps exceeding 1,400 feet of Lower Pottsville appears to be 

 sweeping westward with relatively slow diminution toward the Missis- 

 sippi line and the great embayment. 



EASTERN MARGIN OF THE BASIN 



Respecting the eastern margin of the Pottsville basin, there is room 

 for great difference of opinion. It would seem, however, that the deep 

 basin at the present margin of the southern Anthracite field must have 

 been near the scene of orogenic movement. In the Southern Appa- 

 lachian region the coarsely conglomeratic material is less both as to size 

 and relative amount, though the extent of the formation is far greater. 

 On account of the absence of residual masses of Pottsville in the Clinch 

 Mountain syncline of southwest Virginia, Mr M. R. Campbell is disposed 

 to believe that the Pottsville did not extend as far east as Clinch moun- 

 tain in the Estillville quadrangle. On the other hand, the rapid loss of 

 the beds up to and including the Bon Air-Raleigh within a relatively 

 short distance from the eastern margin of the field f shows that the axis 

 could not have lain far westward along a zone extending nearly to the 

 latitude of the center of the Warrior coal field. In the opinion of the 

 writer, the basin in early Pottsville time extended a considerable dis- 

 tance to the eastward of the present coal-field limits in the Southern 



*The reported thickness of the Pottsville in the Broad Top field, if accurate, would seem to 

 locate that area on the verge of the overlap of the eastern Sharon as illustrated on the map. 

 fSee M. R. Campbell : Huntington, Standing Stone, Richmond, and London folios. 



