148 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



kiA R 7 HA S VMe YARD 



Azores 



Soo Miguel 



■ *—» sZ'JSfi" emum* 



moo nmous 



Fig. 10.12. Relief profiles across the Atlantic. Reproduced from Heezen ef a/., 1959. Letters a to q indicate 

 where sounding profiles of different cruises were joined. 



Flank Provinces 

 Upper Step 

 Middle Step 

 Lower Step 



For further information the reader is referred to the work of Heezen 

 et ah, Geological Society of America Special Papers 65. A tectonic map 

 to supplement the publication is yet to appear, but the gross details as 

 now conceived by Heezen and colleagues of Lamont Geological Labora- 

 tory are portrayed in the cross section of Fig. 10.13. 



Blake Plateau, Blake Bahama Basin, and Outer Ridge 



As shown on Fig. 10.11 the continental shelf breaks into two steps 

 south of Cape Hatteras, and the lower step is known as the Blake Plateau. 



East of the Blake Plateau is the Blake Bahama basin, and east and north 

 of it is the low Outer Ridge. The Outer Ridge swings northwestward at 

 29° N. Lat., 73° W. Long., and heads toward the Cape Fear arch to 

 merge with the Blake Plateau. Details are given on Fig. 10.6. The outer 

 escarpment of the Blake Plateau is probably a fault scarp, according to 

 Heezen et al. ( 1959 ) . See lower diagram of Fig. 10.7. 



A seismic refraction survey of part of the Blake Plateau was made by 

 Hersey et al. ( 1959 ) , and the principal profiles are shown on Fig. 10.6. 

 The same letter designations are retained for the profiles as in the original 

 article. The purpose of the study was to determine the relation of the 

 Plateau crust to the continental crust on one side and to the oceanic crust 

 on the other. Four characteristic profile sections are shown in Figs. 10.14 

 and 10.15. 



