580 E. W. SHAW AGES OP APPALACHIAN PENEPLAINS 



described by Hayes, or even the several later referred to by Hayes. For 

 example, in the Eoan Mountaiu folio he speaks of four peneplains which 

 are represented in the one quadrangle, although he does not state their 

 age. 



Although some folios refer to the age of the peneplains in general 

 terms only, some are more specific. For example, in a late folio Camp- 

 bell, Clapp, and Butts^^ say : ^ 



"Evidence of at least one cycle of erosion and of subsequent uplift in tlie 

 Mesozoic era is preserved in the Appalachian province. 



"The old peneplain can be traced eastward and southward, and in New Jer- 

 sey and Alabama passes beneath deposits of early Cretaceous age. This fact 

 proves that the peneplain was completed and submerged around its margins 

 previous to earlj- Cretaceous time." 



Thus, according to what treatise one chances to pick up, he may infer, 

 with more or less uncertainty, that the Cretaceous peneplain was com- 

 pleted some time before the opening of the Cretaceous period and was 

 remodeled by the advancing Lower or Upper Cretaceous sea, or that it 

 was completed at one time or another in this long period, or even in the 

 early part of the following Tertiary. Many writers are not explicit and 

 precise; some, perhaps, because they believe the information insufficient 

 to warrant exact dating of the surface. In any case the most prevalent 

 impressions seem to be that the Cretaceous, Kittatinny, Schooley, and 

 Cumberland peneplains are approximately equi\alent in age and slope 

 down below the Cretaceous system of deposits, and that the Tertiary, 

 Summerville, Highland Eim, and Shenandoah are equivalent and their 

 development occupied the latter part of Cretaceous and the early part of 

 Tertiary time. 



The statements regarding the ages of the Appalachian peneplains, 

 though somewdiat indefinite, seem to have been accepted almost without 

 question or critical examination. They are repeated in a multitude of 

 publications and are used as perfectly good foundation material for other 

 inferences. 



Peneplains many hundred miles awa}', and far beyond the limits of 

 continuous tracing, have been correlated with the Appalachian peneplains. 

 In northwestern Illinois, Hershey^^ and Bain-*^ describe peneplains of 

 Tertiary and probable Cretaceous age. 



18 M. R. CampbeU, F. G. Clapp, and Charles Butts: P. S. Geol. Survey Geol. Atlas, 

 Barnesl)oro-Patton Folio, No. 189, 101.^, p. 9. 



!» O. II. Hersliey : Pre-Glacial erosion cycles in northwestern Illinois. Am. Geol., vol. 

 18, 1890, p. 72. The physiographic development of the upper INIississippi Valley. Am. 

 Geol., vol. 20, 1897, pp. 246-2G8. 



20 H. F. Bain : Zinc and lead deposits of the upper Mississippi Valley. U. S. Geol. 

 Survey Bulletin 294, 1906, pp. 1-5 and 16. 



