EVIDENCE AS TO AGE 



583 



standing of the inferences concerning the ages of the peneplains, for in 

 the first place it Avould simply destroy the principal line of evidence as to 

 their age, and in the second it could scarcely account for an abrupt down- 

 bend along the original margin of the Cretaceous and Tertiary deposits, 

 and surely not along what happens to be their present margin, for this is 

 continually shifting seaward. It may be argued tliat since remnants of 

 the so-called Cretaceous peneplain are scarce in a belt bordering the 

 Coastal Plain, it may have been uplifted in this belt, so as to give it a 

 greater slope on the seaward portion of the belt and make it harmonize 

 with the peneplain under the Cretaceous deposits. This also would set 

 aside the line of evidence generally regarded as most valuable, namely, 

 that concerning coincidence of jorojected planes. If the possibility is real, 

 then we must at least abandon such inferences as that the Cumberland 

 and sub- Cretaceous peneplains are the same, for any other correlation 

 would be as reasonable. On the other hand, since, with the possible ex- 

 ception of the Nashville dome, which has been slightly uplifted, and a 

 district just west of Washington, D. C, there is little indication of differ- 

 ential uplift in the Piedmont province and other portions of the border- 

 ing belt; the general discordance in positions and slopes of plains that 

 have been correlated requires presumably some other explanation. 



The following table shows the general form and extent of the Coastal 

 Plain deposits: 



EXTENT OF ATLANTIC COASTAL PLAIN DEPOSITS 



Place througfh which section 

 is taken. 



Approximate 

 altitude 

 at inner 

 border. 



Distance from inner border 

 to- 



Present 

 coast. 



300-foot ! 2400-foot 

 50-fath.) j(400-fath.) 

 contour, contour. 



Thickness of 



deposits 



at present 



coast. 



Southern New Jersey .... 



District of Columbia 



Norfolk, Va 



Wilmiugton, N. C 



Charleston, S. C 



Savannah, Ga 



Montgomery, Ala., and 



Pensacola, Fla 



Approximate ( average ) . . . 



Feet 

 200 

 400 

 250 

 275 

 425 

 400 



550 

 400 



Miles 



Miles 



60 



130 



120 



160 



90 



155 



115 



175 



125 



170 



125 



195 



165 



200 



115 



170 



Miles 



140 



175 



160 



205 



255 



240 



250 

 200 



Feet 



2,000± 



2,500? 



2.500± 



1,600± 



2,500± 



2,500?=^" 



4.000? " 

 2,500 



The figures in the above table are believed to represent correctly the 

 general cross-section form of the land portion of Coastal Plain deposits 



23 According to T. W. Vaughan and L. W. Stephenson, perhaps somewhat too low (oral 

 communication ) . 



