F-3 



on-bottom towing of the canyon sled. The sled was equipped 

 with a digital pressure gauge and another 12 kHz sound 

 source in order to provide a limited subbottom definition 

 and a crisp bottom profile undistorted by side-echoes. Many 

 of the sled tracks were oriented parallel to the contours 

 for the purpose of crossing canyon tributaries. The tribu- 

 taries have only minor relief of a few meters to a few tens 

 of meters, but along the canyon walls they are boldly in- 

 cised as V-shaped gullies. The only tributaries with flat 

 floors are the major ones originating on the slope outside 

 the canyon area or those having a distant seaward confluence 

 with the main canyon. Such major tributaries have their own 

 second and third order tributaries. 



Sediment sampling of continental margin outcrops and 

 surface veneer has long suggested that these materials con- 

 stitute the submarine extension of coastal plain formations. 

 Basement rocks of the East Coast are pre-Carboniferous meta- 

 morphic and igneous rocks, and down-faulted troughs filled 

 with Triassic rocks (Emery and Uchupi, 1972). Unconformable 

 on this basement are consolidated Jurassic to early Pleisto- 

 cene sediments blanketed by a late Pleistocene to Holocene 

 cover of unconsolidated sediment. Drake et al. (1959) , in- 

 terpreting deep seismic refractions north of Cape Hatteras, 

 delineated two linear accumulations of sediments, one under 

 the present shelf and one under the base of the slope. They 

 inferred that the sedimentary accumulation beneath the shelf 

 was comparable with the classic miogeosynclinal struc- 

 tures while the accumulation near the slope might be the 



