Seismicity continental margin, 51 epicenter map, North Atlantic, facing page, 122 Mid-Atlantic Ridge, 98 ocean-basin floor, 80 Seismic-reflection measurements, 80 Seismic-refraction measurements continental margin, 52, 81, 102 Mid-Atlantic Ridge, 81, 100, 102 ocean-basin floor, 65, 80, 81, 102 Serpentine, 99 Serpentization, 103 Setúbal Submarine Canyon, 37 Sharks tooth, photograph of, facing page, 39 Shelf break, 17, 50, 51 Sierra Leone Rise, 61 Slumping, 50, 51, 99, 105 Sohm Abyssal Plain, 55, 56, 57, 71, 72, 74 Sound velocity corrections, 12, 13 Sounding corrections slope, 15 velocity, 12, 13 Sounding tracks nonprecision, 7 PDR, 6 Sounding velocity, 12 Soundings echo, 8, 9 hemp line, 8 wire, 8 South Atlantic, Physiographic Diagram, v South Canary Basin, 12 Southeast Newfoundland Ridge, 22, 63, 67, 70, 71, 72 Sub-bottom echoes, 25, 32, 41, 105-106 Submarine canyons, 20 Cape Breton, 37 Fosse de Cayar, 41 Gilbert, 44 Grand Banks, near, 23 Hudson, 8, 27, 28, 30, 31, 58, 72 Hydrographer, 45, 46 Lisbon, 37 Lydonia, 44 Nazaré, 37 Northeast Providence, 35 Oceanographer, 44, 45, 46 Setúbal, 37 Starfish, photograph of, facing page, 39 Structural benches, 43, 48, 49 Submarine topography, outline of, 15 Sunken islands, 78 Tagus Abyssal Plain, 56, 57, 61 TALISMAN, Research Vessel, 99 Tectonic map, Atlantic Ocean, 2 Tectonic uplift, 77, 78, 98 "Terraced zone", 95 Terraces, continental shelf, 42 Tertiary ocean-bottom temperatures, 106 Tertiary outcrops, 46, 47, 48, 76, 79, 107 THETA, M/V, (sealer), vii, 72 Theta Gap, 66, 72, 73, 74 Times Facsimile Company Precision Depth Recorder, 8, 9 Tracks and trails, photographs of, facing pages, 39, 79 Trench (Abyssal) Plains Cayman, 56, 60 Kurile-Kamchatka, 60 Middle America, 60 Peru-Chile, 60 Puerto Rico, 17, 36, 52, 56, 60 Trilobites, Mid-Atlantic Ridge, 99 Turbidity currents, 23, 50, 51, 74, 79, 80, 99, 106, 107 Unconformities, 50 U. S. Coast Survey, 8 U. S. Navy Bureau of Ships, vii Hydrographic Office, 5 Office of Naval Research, vii Units: depth, slope, distance, 12 Upper Step, 15, 78, 90, 91, 94, 95, 96 Vema Gap, 58, 60, 66, 72, 74 VEMA, Research Vessel, vii, 6, 72 Virgin Islands Bank, 36 Volcanic cones, buried, 51 Volcanic detritus, 53 Volcanoes, 39, 77, 78 West Europe Basin, 12 West Florida Escarpment, 33 Woods Hole Oceanographic Institution, vii, viii, 3, 7 Yorktown (Miocene) formation, 44, 45, 46 [Illustration: Heezen _et al._, PL. 20 PHYSIOGRAPHIC PROVINCES, ATLANTIC OCEAN</a>] [Illustration: Heezen _et al._, PL. 21 CONTROL CHART