Submarine canyons cut across all the continental-margin provinces except isolated portions of the outer ridge. Submarine canyons range from less than a mile to more than 10 miles in width and from less than 10 to nearly 1000 fathoms in depth. Canyons are most abundant on the continental slope. However, a smaller number persist across the continental rise. They are also found on the marginal escarpments and on the landward slopes of trenches. Shepard (1948), Kuenen (1950), Veatch and Smith (1939), De Andrade (1937), Johnson (1939), and others have discussed the continental-slope canyons at great length. Canyons in the continental rise of the North Atlantic were discovered and mapped by Ericson, Ewing, and Heezen (1951). REGIONAL DESCRIPTION OF CONTINENTAL MARGIN This discussion is based on continuously recorded echo-sounding traverses made by Lamont Geological Observatory expeditions. Profiles approximately perpendicular to the continental margin are reproduced in Plates 24 and 25. None is precisely perpendicular, and thus slight distortions of slopes and widths of the features are unavoidable. EASTERN NORTH AMERICA: Thirty-four profiles of the continental margin of eastern North America are presented in Plate 24. The positions of the profiles are indicated on the index chart in Plate 23. All profiles show the three categories of continental-margin provinces. Profiles W-1 to W-21 Plate 24 show the more general succession of shelf, slope, and rise, while profiles W-22 to W-34 show the outer ridge-marginal basin and outer ridge-marginal trench complexes. Each of the 34 profiles exhibits a continental shelf although it may range from 20 to 300 miles in width. On each a shelf break is present at depths of 20-150 fathoms. Each profile shows a continental slope, the base of which may be from 300 to 1900 fathoms deep. Northern Grand Banks Sector.--On profiles W-1 to W-6 (Pl. 24), across the Grand Banks of Newfoundland, the shelf ranges from 120 to 285 miles in width. Exceptionally strong local relief of 50-100 fathoms is found on the shelf in profile W-1 northeastward from Newfoundland. The shelf break, which occurs at 150 fathoms, is abnormally deep--more than twice the depths found off New England. The continental slope has a typical gradient of 1:20 but is unusually short as the continental rise is reached at 725 fathoms. From this depth the continental rise descends to the 1700-fathom curve at a gradient of 1:140. This gentle slope is interrupted by a group of exceptionally rugged lower continental rise hills which rise to 1250 fathoms. Northeast of the hills the 2200-fathom line marks the rather abrupt beginning of the abyssal plain which slopes seaward at a gradient of 1:1100.