Mid-ocean canyons or features resembling them have been found in the Indian Ocean Bay of Bengal (Dietz, 1953), in the northwest Atlantic (Ewing _et al._, 1953), the western Atlantic, and the equatorial Atlantic (Beckmann, in preparation). Gibson (1958) has reported one in the Gulf of Alaska. Three in the Atlantic and one in the Gulf of Alaska have been mapped. Although mid-ocean canyons probably join with continental-margin submarine canyons, no such connection has been mapped. Menard (1955) has recorded from the North Pacific several crossings of features resembling the mid-ocean canyons of the Atlantic, which he refers to as deep-sea channels. * * * * * _Regional description._--Abyssal gaps and mid-ocean canyons are found in both the western Atlantic and eastern Atlantic. [Illustration: FIGURE 29.--_Northwest Atlantic Mid-Ocean Canyon_ Surveyed positions and extensions; generalized bathymetry simplified from Smith, Soule, and Mosby (1937)] [Illustration: FIGURE 30.--_Eight east-west profiles showing Northwest Atlantic Mid-Ocean Canyon_ Soundings obtained with NMC sounder run with precision controlled ac power in 1949] [Illustration: FIGURE 31.--_Forty-eight cross sections of Northwest Atlantic Mid-Ocean Canyon_ Soundings originally recorded on UQN-1B sounder with precision controlled ac power in 1952] [Illustration] WESTERN ATLANTIC: The major abyssal plains of the western Atlantic are connected from north to south by a series of abyssal gaps and mid-ocean canyons. The Northwest Atlantic Mid-Ocean Canyon (Fig. 29) begins in an unknown area north of the limit of the physiographic diagram (Ewing _et al._, 1953). It runs south parallel to the continental margin of the Grand Banks on the west and to the Mid-Atlantic Ridge on the east until it reaches the Southeast Newfoundland Ridge, where it cuts through a narrow abyssal gap. After passing through the gap, the canyon turns west, broadens, and is finally lost in the Sohm Abyssal Plain. The mid-ocean canyon is about 3 miles wide and 50 fathoms deep north of the Southeast Newfoundland Ridge (Fig. 30). The west wall is about 10-15 fathoms higher than the east wall (Fig. 32). The canyon has been mapped by more than 80 echo-sounding profiles (Fig. 31). The average slope of the sea floor at right angles to the axis of the canyon in most places exceeds the gradient of the canyon. The gradient west to east is about 1:1500, while the gradient of the canyon from north to south is 1:2250. [Illustration: FIGURE 32.--_Long profile of Northwest Atlantic Mid-Ocean Canyon_ Numerals I-VIII indicate location of profiles of Figure 30.] The mid-ocean canyon forms gentle meanders (Fig. 29). As the gradient of the canyon decreases, the canyon changes its cross-section form from a narrow, deep canyon to a broad, shallow one (Figs. 31 and 32).