268 D. WHITE — DEPOSITION OF APPALACHIAN POTTSVILLE 



period. The present paper is, however, to be regarded as preliminary, 

 or as a mere report of progress, and therefore subject to further revision 

 on the completion of the paleobotanical studies. 



The Mississippian-Pennsylvanian Unconformity 



The existence of an unconformity at the base of the Pottsville series 

 in the Appalachian trough was, I believe, first proposed and insisted on 

 by Dr I. C. White,* who remarked the absence of the Sharon conglom- 

 erate at points in the northern portion of the Ohio coal field and at sev- 

 eral localities near the state line in western Pennsylvania, although in 

 general the thin northern bituminous sections are treated by him as 

 equivalent in time to the entire thickness of the Pottsville sediments in 

 the Southern Anthracite field or the eastern Kentucky coal field.f The 

 exact equivalence of the thick and thin Pottsville sections in Pennsyl- 

 vania is distinctly set forth in the later reports of the state geologists, 

 while the evidence of unconformity is described as obscure and unim- 

 portant.! 



The study of the fossil plants has shown that the Sharon conglomerate, 

 which constitutes the basal member of the Upper Carboniferous over 

 the greater portion of western Pennsylvania and in Ohio, and which has 

 been regarded as the basal member of the Pottsville in general, belongs 

 in the upper part of the typical Pottsville, and that several thousands of 

 feet of Pottsville sediments in the Southern Appalachian region and a 

 great thickness of beds in the Southern Anthracite basin were laid down 

 before an encroaching sea began the assortment of Sharon material in 

 western Pennsylvania or Ohio. I 



Figure of the Basin and Thickness of Pottsville Sediments 



The nature and extent of the unconformity and the relative thickness 

 of the sedimentation are at once graphically indicated in the accom- 

 panying map and stratigraphic profiles. On the map (plate 11) the 

 original thickness of the Pottsville sediments in different portions of the 

 Appalachian Upper Carboniferous coal fields is indicated by 100- foot 

 contours. Assuming that the topmost bed of the series is horizontal, 

 the contouring, verging downward, shows in somewhat generalized form 



*Bull. U. S. Geol. Survey, no. 65, 1886, pp. 22, 68, 69. 



Rept. Geol. Survey of West Virginia, vol. ii, 1903, p. 610. 

 fBull. U. S. Geol. Survey, no. 65, p. 202. 



{Summary Final Rept., iii, pt. 1, pp. 1807, 1809, 1857, 1858, 1864. 

 g Bull. Geol. Soc. Am., vol. 6, 1895, p. 319. 



Twentieth Ann. Rept. U. S. Geol. Survey, 1900, pt. 2, pp. 819, 820-823, 917. 



