248 J. Barrett — Upper Devonian Delta of the 



have held rather closely to the present margins of the con- 

 tinental platforms. In the absence of evidence of a former ex- 

 tension of the land beyond these margins this procedure is no 

 doubt the wisest and without it as a point of departure each 

 different map would represent guess work and not science. 

 But undue importance finally becomes attached to a conclusion 

 for which there is onty negative evidence. Thus it has been 

 customary to regard the land of Appalachia, which through the 

 Paleozoic shed sediments westward into the geosyncline, as 

 confined to the area of the present continental platform, 

 although from Nantucket to North Carolina the submerged 

 shelf to the hundred fathom line is but approximately 75 to 80 

 miles in width. 



Breadth of Appalachia implied by the Volume of Sediments. 



The present investigation tends to limit the fields of erosion 

 during the Upper Devonian to those ancient terranes now 

 hidden beneath the Coastal Plain and the sea, leaving a width 

 of not more than 125 miles opposite Pennsylvania to supply 

 the great volume of sediments. In fact, if it be assumed of 

 such a marginal region that half of its width shed its waste 

 eastward into the Paleozoic Atlantic, it leaves a maximum width 

 of but 60 miles, to have yielded the sediments which in the Upper 

 Devonian alone were greater in volume than the entire Sierra 

 Nevada. Over New England the available zone within the 

 limits of the continental platform was much wider, but reasons 

 have been given for believing that a large supply of the Upper 

 Devonian sediment of Pennsylvania and Maryland came from 

 the east and southeast. 



If the present margin of the continental platform has held 

 approximately its present place since the Upper Devonian, as 

 many paleogeographic maps imply, it means, allowing for a 

 certain breadth of shelf at that time, that Appalachia must 

 have been still further restricted in width. Asa quantitative 

 test of such a view assume Appalachia from Rhode Island to 

 Virginia to have been a mountain system 100 miles wide. 

 Consider it an isosceles triangle in vertical cross section, and 



• -r 



giving as much waste to the east as to the west. The Upper 

 Devonian sediments between lat. 39° 30' and 43° and east of 

 long. 80° 30', approximately the limits of the map, fig. 1, 

 are computed to have had an original volume of 63,000 

 cubic miles. Neglecting the outlying portions, although 

 these are of great thickness in West Virginia ; assume that 

 this sediment is equal to the volume eroded from the western 

 side of Appalachia over a length of 500 miles, from southern 

 Maine to the coast of southern Virginia, — the sediment thus 

 converging into the geosyncline. The computation shows 



