O -J 



S§y 



a I- 



a Z3 



a I <; 



<: I- 2 



2 en 



gen 

 en 



^0 O.l 0.4 0.6 0.8 1.0 I.Z 1.4 1.6 t.& 2.0 Z.Z 2.4 26 2.3 



MEAH DISTANCE BETWEEN TRACKLINES 

 (NAUTICAL MILES) 



Figure 6. — Variation of tlie standard deviation of the 

 isobath position error with resiject to the mean distance 

 between tracklines. 



coastal plain and continental shelf. This plain be- 

 came an epicontinental inland sea in post-Ordo- 

 vician times, and its bottom was progressively 

 folded mitil the Appalachian Eevolution of middle 

 and late Permian times finally forced it and its 

 sediments into the present Folded Appalachian 

 Moimtains. The above sequence of events is only 

 one recent inference from available evidence; for 

 other interpretations of the geologic history of the 

 region see Schuchert (1923), Kay (1951), Drake 

 etal. (1959), Wilson (1966), and Harland (1967); 

 seealso the criticism by Hsu (1965) of earlier ideas 

 of Dietz (1963a) and the reply by Dietz (1965). 



-^.S v''-^  ' 





Figure 7. — Physiographic regions of the Middle Atlantic Coast. (1) Appalachian Plateaus and Interior Lowlands. 

 (2) Folded Appalachian Mountain-s. (3) Older Apiwlachian Moimtain.s, including (3A) Blue Ridge Mountains, 

 (3B) New England-Acadian Mountains, (3C) Piedmont-Xew England Hills, (3D) Piedmont Plain, and (3E) Xew 

 England Plain. (4) Emerged and Submerged Coast.al Plain, including (4A) Emerged Coastal Plain, (4B) Sub- 

 merged Coastal Plain or Continental Shelf, and (4C) Gulf of Maine Basin. (5) Continental Sloi>e. (6) Continental 

 Rise. Boundaries are approximate. Sources: Femieman (1938) ; Heezen et al. (1959) ; and Hammond (19<>4). Tlie 

 heavy solid line is the boiuidary of the mapped area. 



50 



U.S. FISH AND WILDLIFE SERVICE 



