PART 2. PHYSIOGRAPHIC PROVINCES 11 Introduction 11 Nomenclature and classification of deep-sea relief 11 Units of depth and slope 12 Continent and ocean 16 Continental margin 17 Definition and general categories 17 General categories 17 Category I provinces 17 Category II provinces 18 Category III provinces 19 Regional description of continental margin 21 Benches and terraces of the continental margin 41 Geology and geophysics of continental-margin physiographic provinces 51 Seismicity of the continental-margin provinces 51 Magnetic anomalies and continental-margin physiographic provinces 51 Crustal structures and continental-margin provinces 52 Sediment distribution and physiographic provinces of the continental margin 53 Past, present, and future of the continental-margin provinces 53 Ocean-basin floor 55 General description 55 Abyssal plains 55 General discussion 55 Regional description 57 Abyssal hills 61 Definition and distribution 61 Regional description 63 Origin of abyssal-hills topography 65 Other major features of the abyssal floor 66 Abyssal gaps 66 Mid-ocean canyons 66 Regional description 66 Origin of abyssal-floor topography 74 Oceanic rises 74 Definition and distribution 74 Regional description 74 Seamounts of the ocean-basin floor 78