EROSIONAL HISTORY OF DRIFTLESS AREA 123 



(6) The gravels of the Driftless Area are strikingly similar 

 to the Tertiary gravels of the Gulf region. (7) There are 

 numerous patches of similar deposits south of the glaciated 

 area and beneath the drift which seem to connect the gravel 

 formation of the Driftless Area with the Tertiary deposits 

 of the Gulf Coast. (8) The Dodgeville plain on which the 

 gravels lie slopes south toward the Tertiary deposits rather 

 than west toward the Cretaceous. (9) Salisbury's inter- 

 pretation has been in print for a quarter of a century and 

 all new discoveries seem to corroborate his tentative conclu- 

 sions. (10) All patches of gravel between the Driftless Area 

 and known Tertiary deposits occupy summit areas in the top- 

 ography. (11) If the base of the Tertiary deposits were 

 projected north it would coincide roughly with the Dodge- 

 ville plain. (12) The base of the Tertiary deposits is in 

 itself a peneplain. (13) The Tertiary gravels are known 

 to lie on a raised peneplain in the southern Appalachians 

 and elsewhere. These facts seem to the writer almost con- 

 clusive of the Tertiary age of the Dodgeville plain. Whether 

 the plain is Eocene, Oligocene, Miocene, or Pliocene in age 

 cannot be determined, for the precise age of the Tertiary 

 gravels on the Gulf Coast is in doubt. It is believed, how- 

 ever, to be late rather than early or middle Tertiary. 

 The Age of the Lancaster Plain 



The Lancaster plain is clearly younger than the Dodge- 

 ville plain and is probably therefore late Tertiary or Pleis- 

 tocene in age. It has been generally understood that the 

 great uplift in the interior of the United States came at the 

 close of the Tertiary, in the epoch known by some as the 

 Ozarkian. Because the greatest movement which affected 

 the Driftless Area uplifted and started the dissection of the 

 Lancaster plain this plain has been most generally referred 

 to the late Tertiary. 



The writer is not certain that the Lancaster plain is not 

 Tertiary in age, but he wishes to present some evidences 

 that it was not completed and uplifted before the first ice 

 invasion. The work of the writer during several years, and 

 the work of A. J. Williams' has shown that there is old 



1. Williams, A. J., Manuscript so far unpublished. 



