66 J. J. STEVENSON — PENNSYLVANIA ANTHRACITE. 



almost hydrous coals of Iowa and Missouri and the anhydrous coal of 

 Indian territory. 



The Writer's Hypothesis as to Origin of Coal-beds. 



But we are not left altogether to suggestion in the effort to explain the 

 origin of the Pennsylvania anthracite as resulting from continuous loss 

 of marsh gas until the final burial and consolidation. 



More than twenty years ago the writer, having discovered that the 

 limestones of the Ohio Upper Coal Measures disappear at but a little way 

 west from the Ohio river, was led to assert that the Coal Measures of the 

 Appalachian basin " were not united to those of Indiana and Illinois at 

 any time posterior to the Lower Coal Measures epoch and probably were 

 always distinct." Studies made in the Ohio and West Virginia coal- 

 fields led also to the conclusion that the lower coal-beds had been 

 deposited as fringing marshes,* and that the coal-beds, for the most part, 

 had their origin at the east. It is unnecessary to enter into the details 

 of the theory of the origin of the Appalachian coal-beds presented by the 

 writer in 1872 f and amplified in later publications, as they do not concern 

 the matter at issue here. It suffices that on purely stratigraphic grounds 

 the conclusion w^as reached that the Coal Measures marsh had its origin 

 at the east, and that it extended seaward after each period of accelerated 

 subsidence, so forming a new coal-bed. According to this hypothesis 

 one should find in the northeastern portion of the Appalachian basin 

 not only a greater mass of coal than in any other part of the basin, but 

 also a greater degree of conversion. 



APPLICATION OF THE HYPOTHESIS. 



Thickness of Coal greatest in northeastern Portion of Appalachian Basin. — 

 Let the lower coal group be used first in making comparison of thick- 

 nesses in different parts of the basin. 



The greatest thickness is found in the Southern and Middle anthracite 

 fields and in the eastern portion of each. The variation in the Southern 

 field is from 106 feet of coal X at the extreme east to 18 feet at the extreme 

 southwest. The average at the east is about 58 feet and for the middle 

 about 53 feet. The thickness for the west end is taken from Taylor, but 

 H. D. Rogers § thinks it too great. The Middle field does not extend so 



* Stevenson cited by Newberry, Geol. of Ohio, 1874, vol. 2, part i, p. 169. 



t Stevenson : Annals of Lyceum of Nat. Hist, of New York, 1873, vol. x, p. 252 ; Proc. Amer. Phiios. 

 Society, 1875, vol. xiv, p.293; Second Geol. Survey of Pennsylvania, Rep. on Fayette and Westmore- 

 land District, part ii, pp. 283-295. 



t Ashburner: First Rep. of Progress in the Anthracite Coal-field, 1883, p. 45; Annual Report for 

 1885, pp. 330-339. 



g Rogers : Geol. of Pennsylvania, 1858, vol. ii, pp. 193-195, 



