94 IOWA STUDIES IN NATURAL HISTORY 



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Obviously the Lancaster plain 

 is not an original marine plain of 

 deposition, neither was it formed 

 by marine denudation. Lying as 

 it does here at one stratigraphic 

 horizon and there at another, it 

 cannot be a simple structural 

 plain. Because the Lancaster 

 plain is represented by many 

 broad, flatfish, intermediate sur- 

 faces close enough together to 

 warrant correlation ; because it is 

 distinct from the DodgDville 

 plain ; because it has a general 

 southerly slope ; because its slope 

 is not parallel with the under- 

 lying strata ; because the plain 

 bevels the edges of the strata ; be- 

 cause its surface has about the 

 degree of irregularity and slope 

 which a peneplain should have; 

 because it is not confined to cuesta 

 belts but has a wide distribution 

 in the inter-cuesta areas the Lan- 

 caster plain seems even more 

 surely to be a true peneplain than 

 is the Dodgeville plain. It cannot 

 be held to be a series of unrelated 

 cuestas. The Lancaster plain, 

 therefore, is believed to be a true 

 peneplain, younger than the 

 Dodgeville plain, uplifted since 

 its formation, and now approach- 

 ing thorough dissection in the 

 present cycle of erosion. For an 

 additional illustration of the feat- 

 ures on which this belief is based, 

 see Fig. 26. It should not be 

 understood that this surface was 



