56 STEVENSON— FORMATION OF COAL BEDS. [Ap^-n i8, 



I. C. White*" has given many measurements of the bed showing 

 that similar changes are found in West Virginia along the eastern 

 border, beginning at a few miles south from the Pennsylvania border. 

 The Roof division is wanting almost at once, but that is due to 

 erosion prior to deposition of the Pittsburgh sandstone, and at times 

 one finds the bed complete where the roof was spared. At a little 

 distance southwest, where the sandstone has thinned away, the 

 changed section is distinct and the bed appears to be merely double. 

 It is divided by " bone " or clay, i to 15 inches, and the benches vary 

 greatly in thickness ; at some localities the upper one has almost dis- 

 appeared while at others the lower is almost wanting; here and there 

 the bed has a section somewhat like that at the north but comparison 

 of the parts shows that the resemblance is only apparent. The 

 writer, nearly 40 years ago, thought that the change was merely 

 apparent and that he could recognize all elements of the northern 

 structure to a great distance south from Pennsylvania ; but the many 

 detailed measurements recorded by White make that position no 

 longer tenable. 



Study of measurements along the northern border of the bed prove 

 a variability which was not considered important by the students 

 who examined that area. W. G. Piatt's"*^ sections in Indiana county 

 of Pennsylvania show that in the extreme northern outliers along 

 the eastern side, the structure is clear, but the lower members are 

 irregular, becoming indefinite at times, while the Breast-coal in- 

 creases in importance. Measurements recorded by White and by 

 Stevenson*^ in Allegheny and in northern Washington county show 

 that in the outlying areas at the north, the structure is usually 

 recognizable but that the bottom and brick are insignificant, the 

 bearing-in not always distinct, while the breast, though variable, is 

 the important portion. These changes are wholly in contrast with 

 those already noted as occurring at the south in both Ohio and West 



"L C. White, Geol. Surv. West Virginia, Vol. II., 1903, pp. 168-190; Vol 

 II. a, 1908, pp. 659, 663, 665, and elsewhere. 



" W. G. Piatt, Sec. Geol. Surv. Fenn., Rep. HHHH, 1878, pp. 162-164, 27. 



"I. C. White, Sec. Geol. Surv. Fenn., Rep. Q, 1878, pp. 152, 166, 177; 

 J. J. Stevenson, ibid., Rep. K, 1876, pp. 275, 277, 285; Rep. KK, 1877, pp. 

 313. 322. 



