54 J. J. STEVENSON — PENNSYLVANIA ANTHRACITE. 



cataclysmic and deep-seated. Nothing need be said at this stage respect- 

 ing the former, but reference to the latter is necessary. 



Appalachians not caiadysmic in Origin. — Possibly the writer may have 

 been wrong in imagining that the plication advanced so slowly as not 

 to interfere with the main water-courses/^ but the drainage in Pennsyl- 

 vania, Maryland, Virginia and West Virginia certainly suggests that the 

 more important streams antedated the folds, for they cross and recross 

 the great anticlinals, synclinals and faults by gaps, in whose walls the 

 rocks are true to dip and strike. Another explanation is possible with- 

 out calling in the aid of cataclysms. The plication was not so slow 

 everywhere as to permit readjustment of the rock particles without crush- 

 ing. The great Pocono sandstone in Fulton county of Pennsylvania, 

 more than 1,000 feet thick, was broken into enormous wedges, which 

 were moved one on the other until the contact surfaces were polished, 

 the irregular crevices remaining being filled afterward by thin films of 

 quartz, sufficiently distinct wherever the sandstones are exposed.f The 

 Utica shale in the Great valley of Pennsylvania, as shown in the ap- 

 proaches to the tunnels of the South Pennsylvania railroad, is crushed 

 into lenticular fragments, now polished and closely packed together. In 

 some of the Broad Top mines the coal has suffered similar treatment, 

 with the same result. Such crushing occurs rarely in the less sharply 

 folded area west from the Alleghany, but even there is not altogether 

 wanting, for the coal is often prismatic and jointing is frequently so ex- 

 tensive as to injure sandstone for building purposes. 



But G. K. Gilbert J asserts that this crushing cannot extend deeply ; 

 that there is little possibility of its reaching downward e-ven to ten miles ; 

 certainly, then, the fissuring would not be deep enough to afford escape 

 for heated vapors and gases from the interior of the earth. 



The plication, resulting in the Appalachian revolution, began at an 

 early date, as is evident from existence of canoe-shajoed synclinals, dating 

 back to the middle Coal Measures, and of subaerial erosion, sometimes 

 of great extent in Ohio and' Pennsylvania Coal Measures. Indeed, the 

 folding began far back in geologic time, and the Appalachian basin, 

 closed, it may be, only by a long bar at the west during the Devoni^an, 

 was crumpled in the latter part of that age just as it was during the 

 early and middle Carboniferous, though less extensively. § 



* Stevenson : Proe. Amer. Philos. Society, vol. xviii, 1879, p. 306. 



t Stevenson : Proc. Amer. Philos. Society, vol. xxi, 1884, p. 165. 



J Gilbert: Bulletin of the Geol. Soc. of Amer., vol. i, 1890, p. 27. 



§ For facts referred to in this paragraph see Newberry : Geol. Survey of Ohio, vol. 2, part 1, 1874, p- 

 117; M. C. Reid : Geol. Survey of Ohio, vol. 3, part 1, 1878, p. 572 ; Stevenson : Annals Lye. Nat Hist. 

 N. Y., vol. X, 1873, p. 235 ; also in Second Geol. Survey of Penn., Fayette and Westmoreland District, 

 part 2, 1878, pp. 271-282. 



