464 W. J. McGee — Three Formations of 



sent — throughout the Piedmont region ; and lines drawn in 

 any direction through the area give ever-varying but harmoni- 

 ous combinations of this profile. During recent years this 

 peculiar configuration has attracted the attention of nearly all 

 geologists who have worked in the area. Stevenson has attrib- . 

 uted the broad intermontane plains of the Pennsylvania Ap- 

 palachians to wave-action during, and their minor irregularities 



MONTOVR FUDGE 



Cross-Section of Susquehanna Valley between Bloomsburg and Rerwick. 



to spasmodic elevation following, a general submergence, and 

 ascribed the incised valleys to the action of the streams now 

 occupying them during a recent epoch of high land ;* Kerr 

 attributed the corresponding plains of the Piedmont region in 

 North Carolina to glacial action during a remote epoch ;f G. 

 F. Wright ascribes certain of the plains along the western 

 slope of the Appalachians to a temporary ice-dam in the Ohio 

 Valley \% I. C. White recently referred the deposits upon these 

 plains, if not the plains themselves, as exhibited along the 

 Appalachian rivers, to submergence probably coeval with 

 northern glaciation ;§ but Gilbert has pointed out (orally) that 

 in Virginia and North Carolina, at least, the system of inter- 

 montane plains represents an old base-level of erosion. The 

 composite Appalachian profile indeed indicates clearly that at 

 some period of the past the Piedmont- Appalachian area stood 

 low until the rivers, their affluents, the rivulets leading into 

 these, and even the minutest rain-born rills, cut their channels to 

 base level and planed all the rocks except the obdurate quartz- 

 ites and sandstones to the same level ; and that afterward the 

 land was lifted until the waters attacked their channels, cut 

 out the labyrinth of recent gorges, and reduced the valleys, 

 but not the hills, to a new base-level This degradation-record 

 is as definite and reliable as any found within deposits ; and 

 while so little is known of the physical relations of the clastic 

 deposits of the Coastal plain (though they have been system- 

 atically classified repeatedly upon other bases) that they tell us 

 less than the Piedmont hills of the evolution of the continent, 



* Proc. Am. Philos. Soc, vol. xviii, 1879, 315-816. 



f This Journal, III, vol. xxi. 1881, 216-19. 



\ Am. Nat., xviii, 1884, 563-7. 



§ This Journal, III, xxxiv, 1887, 374-81. 



