APPALACHIAN FOLDS OF CENTRAL PENNSYLVANIA 241 



County the peneplain rises to approximately 1,500 feet above the 

 railroad. As the measurements were all made from the railroad, 

 this correction for the height of the Kittatinny base-level above it 

 should be subtracted from the total height of the folds. Here then 

 are two corrections of opposite sorts, one positive and the other 

 negative. While the figure for the positive correction would seem 

 likely to be somewhat in excess of the figure to be subtracted, there 

 is no good basis for close figuring, and the safest thing, on the whole, 

 seems to be to allow the present height of the peneplain above the 

 railroad which served as a base-line for collecting the data and con- 

 structing the cross-section, to offset what younger strata there may 

 have been above the Pottsville conglomerate. Measuring then from 

 the railroad-level, at which the data were collected, to the top of the 

 Pottsville should give, perhaps, as good an approximation to the 

 height of the original folds as a similar measurement from the Kit- 

 tatinny peneplain to the more uncertain upper surface of the Upper 

 Barren Measures. These more convenient and readily available 

 measuring-points will therefore be taken. 



If, however, one should prefer to strike a general average for the 

 thickness of these measures over the various neighboring areas where 

 they now occur, and to assume that this full thickness of strata covered 

 the whole extent of the Tyrone-Harrisburg section, he may readily do 

 so. From the data given by Stevenson,^ a figure of 1,700-1,800 feet 

 would seem a fair one to adopt. If 1,100 feet represents the average 

 difference in altitude between the Pennsylvania Railroad and the 

 Kittatinny base-level, there remain, following this assumption, 600- 

 700 feet to be added to the estimate of the height of the folded tract 

 to be made shortly. But it is not at all certain that this full thickness 

 of post-Pottsville sediments once extended completely over this area, 

 and, in addition, it would seem that the thicknesses of the various 

 Paleozoics in the reconstructed sections are more likely to be over- 

 estimates than underestimates. Because of a suspicion that possibly 

 somewhat excessive thicknesses may have been allowed for some of 

 the restored formations in the section, the writer prefers not to add 

 this last correction to the total height of the folded belt. 



I J. J. Stevenson, "Carboniferous of the Appalachian Basin," Bull. Geol. Soc. 

 Amer., Vol. XVII, pp. 65-228, and Vol. XVIII, pp. 29-178. 



