586 E. W. SHAW AGES OF APPALACIITAX TENEPLAIXS 



In areas of intense deformation a total reduction of 10,000 to 30,000 

 feet can be demonstrated, vet these are the areas in which surfaces older 

 than the so-called Cretaceons peneplain are said to he preserved. 



If the central part of the province has been reduced from 3,000 to 

 30,000 feet, it seems improbable that any portion of the present surface 

 is even as old as early Tertiary and doubtful if any is a fourth or even a 

 tenth as old as Jurassic or pre-Cretaceous. 



Summary 



Although the published statements concerning the ages of the Appa- 

 lachian peneplains are inharmonious and man}' lack clearness, precision, 

 and supporting evidence, they seem to be accepted with implicit confi- 

 dence. In particular the conclusion that parts of all peneplains developed 

 since Paleozoic time have endured to the present, and that some of these 

 are early Cretaceous or older seems to be unquestioned; yet data which 

 have been generally available indicate that all peneplains of which rem- 

 nants exist today are younger than the floor under the Cretaceous with 

 which one or more have so frequently been correlated, and additional data 

 along several lines gathered during the past ten years support this infer- 

 ence. 



It is the writer's opinion that no portion of any surface so old as early 

 or even late Mesozoic can have endured exposure to the elements in the 

 Appalachian province until the present day, and that the oldest peneplain 

 of which remnants exist was finished in Tertiary time. It seems to him 

 probable that no portion of a surface even so old as Middle Tertiary has 

 been preserved intact without perceptible reduction and remodeling. But 

 however this may be, the evidence as to the ages of the peneplains seems 

 to be fairly harmonious and to indicate ages more recent than those here- 

 tofore assigned. 



