260 Willis and Hayes — Conditions of 



ness of strata deposited on the great limestone. Thus in 

 Lycoming county, Pennsylvania, the total thickness of strata 

 between the coal measures, XIII, and the Cambro-Silurian 

 limestone is 9700 feet, while in Carbon county it is 23,700 feet. 

 There can be no doubt that the surface on which the coal beds 

 formed was essentially horizontal and it follows that to accom- 

 modate this greater thickness beneath a horizontal datum and 

 above the great limestone the latter must have had an initial 

 dip from Lycoming to Carbon county. This dip amounted to 

 about 200 feet per mile and carried the limestone down 14,000 

 feet lower in the Anthracite region than in the Alleghany 

 region. It was a dip due to vertical subsidence, not to com- 

 pression, and formed the northwestern gentle slope of an 

 original syncline of deposition. 



The stratigraphic sections published by the Second Geo- 

 logical Survey of Pennsylvania when compared in detail indi- 

 cate that each of the anthracite basins is related to an area of 

 maximum deposition in consequence of which the deeper 

 strata assumed the form of an original syncline which later 

 become a syncline of compression. Thus in the Wyoming 

 basin No. XI has a thickness of 150 to 400 feet along the 

 sides but is 1200 feet thick at Shickshinny on the synclinal 

 axis. 



In East Tennessee similar original synclines of deposition 

 have been observed, as that in the Bays Mountains where the 

 Silurian shales increase in thickness from 1800 feet on the 

 western side to 4000 or more near the axis, necessitating a very 

 considerable initial dip. Another is represented in fig. 1, p. 

 259, in which the thicknesses are those observed in a section 

 through Clinch Mountain near Rogersville, Tennessee, but the 

 position of the shore line and the shoreward thinning of the 

 upper strata are hypothetical. In northwest Georgia the 

 increase in thickness by 2000 feet or more in the lower Car- 

 boniferous must have produced an original syncline in the 

 present Armuchee basin. Also on the western side of Mur- 

 phree Valley in Alabama the Lookout sandstone forming the 

 base of the Coal measures is only about 60 feet thick while 15 

 miles eastward it has a thickness of from 600 to 800 feet, indi- 

 cating a sharp syncline of deposition on the line of the present 

 Blount Mountain syncline. The effect of this initial eastward 

 dip upon the structure will be indicated later. 



The original synclines so far mentioned have axes parallel 

 with the general trend of the present axes of compression 

 which they doubtless determined, but in northern Georgia 

 and Alabama there is evidence of an old shore line extending 

 nearly east and west with the accompanying syncline of depo- 

 sition parallel to it on the north. This has doubtless been the 



