An echogram obtained along a track running southeast from Charleston, South Carolina, is reproduced in Figure 1 of Plate 7. The continental shelf extends from the shore at an extremely low gradient to the 25-fathom isobath where a small definite notch marks an increase in gradient to 1:1000. This gradient continues to the 50-fathom isobath where it changes to 1:40. At the 90-fathom curve the gradient increases to 1:120 and continues to 160 fathoms where it finally increases to 1:40. This continental slope drops from 160 fathoms to 280 fathoms where the gradient flattens, and the surface changes from smooth to rough, with hills 10 to 20 fathoms high and half a mile to 1-½ miles wide. These hills, which extend for 4-6 miles along the profile, directly underlie the Gulf Stream. For 50 miles seaward of these hills the ocean floor is irregular between 230 and 300 fathoms. At 90 miles from shore five eastward-facing scarps 10-20 fathoms high form a striking contrast to the generally smooth, gently rolling topography. At 300 fathoms the gradient increases to 1:200, and the sea floor drops for the next 24 miles to 400 fathoms where a few small hills are associated with a drop in the gradient to 1:1000. Southeast of this point the bottom is smooth until at a depth of 430 fathoms a steep scarp drops abruptly 30 fathoms to form a mile-wide depression 20-30 fathoms deep. The southeast side of this feature rises to 445 fathoms, and southeastward of a few 5-fathom scarps the surface of the Blake Plateau becomes smooth. [Illustration: PL. 3 FIGURE 1. UPPER CONTINENTAL RISE FIGURE 2. OBLIQUE CROSSING OF SUBMARINE CANYON FIGURE 3. SMOOTH BOTTOM OF LOWER CONTINENTAL RISE FIGURE 4. LOWER CONTINENTAL HILLS REPRESENTATIVE PDR RECORDS FROM CONTINENTAL RISE OF NORTHEASTERN UNITED STATES] [Illustration: PL. 4 FIGURE 1. SHELF BREAK AND CONTINENTAL SLOPE OFF NEW YORK FIGURE 2. SMALL HILLS ON CONTINENTAL SLOPE OFF DAYTONA BEACH, FLORIDA FIGURE 3. SMALL HILLS IN THE STRAITS OF FLORIDA FIGURE 4. SMALL ABRUPT DEPRESSIONS ON THE INNER PART OF THE BLAKE PLATEAU PDR RECORDS FROM CONTINENTAL SLOPE AND BLAKE PLATEAU The positions of all echo-sounding records are shown in Plate 30. Depth in fathoms.] [Illustration: PL. 5 FIGURE 1. WEST OF THE CREST OF THE OUTER RIDGE FIGURE 2. WESTERN SIDE OF OUTER RIDGE NEAR ABYSSAL PLAIN FIGURE 3. BLAKE-BAHAMA ABYSSAL PLAIN PDR RECORDS FROM OUTER RIDGE EAST OF THE BLAKE PLATEAU AND FROM THE BLAKE-BAHAMA ABYSSAL PLAIN Depth in fathoms: The outgoing "pings" as well as "scattering layers" are recorded in the 0-400 fathom scale range; the bottom topography may lie within the range of any multiple of 400 fathoms. The depth scales indicated on the plates refer to the profiles of bottom topography. For example--Figure 1 of Plate 5 shows a 300 fathom deep "scattering layer" over which the bottom profile has been superimposed.] [Illustration: Heezen _et al._, PL. 6