J. Barrett — Upper Devonian Delta, etc. 225 



Art. XVII. — The Upper Devonian Delta of the Appalachian 

 Geosyncline ;* by Joseph Barbell. 



Part III. The Relations of the Delta to Appalachia. 



Introduction and summary — 225 



Indications given by the strata of former extension 226 



Faunal relationships and the possible seaways 226 



Character of the sediments of the marginal outcrops. 229 



Eate of thinning at the present margins 231 



Evidence from the Green Pond Mountain region 234 



Eelations of piedmont gravels to climatic and crustal 



movements 239 



Volume and sources of Upper Devonian sediment 243 



Lack of relation of Appalachia to the continental shelf . . 247 

 The control by the continental shelf on paleogeo- 



graphic maps 247 



Breadth of Appalachia implied by the volume of sedi- 

 ments -. 248 



The shelf a terrace of post-Paleozoic construction 249 



The ocean basins widened by continental fragmenta- 

 tion 252 



Conclusion on Appalachia in the later Paleozoic 252 



Introduction" and Summary. 



The descriptions of the significant formations and the inter- 

 pretations given in the first part upon the delta and its rela- 

 tions to the interior sea follow present well-known paths of 

 geologic thought, but the search eastward and northward for 

 the original boundaries involve interpretations which are much 

 less customary, — interpretations in fact which are contrary to 

 those which have prevailed. A preliminary consideration was 

 therefore necessary in the second part on the factors control- 

 ling the present limits of the strata and the lack of relationship 

 to the original boundaries. This has prepared the ground for 

 the development of the conclusions, resting in part upon evi- 

 dence, in part upon theory, as to approximately what those 

 original limits were, as shown in fig. 1 .f The subject leads 

 up also to the relations of the delta to Appalachia and the 

 information which is given thereby as to the character of that 

 ancient land. 



Briefly, the lines of argument are as follows : The marine 

 fauna of the interior sea shows a connection eastward around 

 Appalachia and implies a far extension, possibly to the south, 

 but more probably to the north, of strata long since broadly 

 uplifted and eroded. The character of the sediments and the 

 rate of thinning at the present margins point to the same con- 

 clusion of a northward extension. The same lines of evidence 



* Continued from this Journal (4), xxxvii, pp. 87 to 109, 1914. 



f Published on p. 430, part I, Nov. 1913, and on p. 89, part II, Jan. 1914. 



Am. Jotje. Sci.— Fourth Series, Vol. XXXVII, No. 219. — March, 1914. 



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