142 



STRUCTURAL GEOLOGY OF NORTH AMERICA 



FROM NEW YORK SOUTHEASTERLY NEARLY TO BERMUDA PEDESTAL 



400 



500 600 



KILOMETERS 



700 



800 



FROM SOUTH OF CAPE CANAVERAL EASTERLY TO BLAKE BAHAMA BASIN, THEN NORTHEASTERLY 



1200 



200 KILOMETERS 400 



500 



700 



1100 



Fig. 10.7. Sections of the crust of the Atlantic Coastal Plain and adjacent ocean. 



shallow valleys. The shelf breaks abruptly at about the 600-foot depth to 

 a steeper slope, known as the "slope" which carries down to 8000 feet and 

 more below sea level in approximately 50 miles. In a few sections, the 

 slope is as steep as 700 feet per mile (732 degrees). 



The slope is riven by two kinds of dip-slope features; canyons that ex- 

 tend headward into the shelf 10 to 30 miles from the outer margin, and 

 numerous deep parallel rills that are limited entirely to the slope. The 

 bottoms of the submarine canyons range from 2000 to 3700 feet below 

 the floor of the shelf at the outer margin. Those south of the submarine 



Hudson channel and canyon generally lose their identity on the slope, 

 merging with the many rill-like canyons or not being larger than the 

 canyons limited to the slope. The Hudson canyon and others that indent 

 the shelf to the eastward along Georges Rank more clearly retain their 

 identity down the slope. Only one submarine canyon in this section of 

 continental shelf can be related with any assurance to a major river on 

 land. This singular relation is the Hudson, whose channel from New York 

 has been mapped about 100 statute miles across the shelf to the head of 

 the deep shelf-indenting and slope canyon. 



