11. Two east-west profiles of Southeast Newfoundland Ridge 22 12. Laurentian Channel 23 13. Eastern Channel, Gulf of Maine 23 14. Submarine canyons off the Scotian Shelf 24 15. Continental-margin provinces: Type profile off northeastern United States 26 16. Tracings of PDR records of continental and insular slopes 28 17. Cross sections of Hudson Submarine Canyon 32 18. Tracing of PDR record of Blake Escarpment 34 19. Continental-margin provinces: Type profiles off northwest Africa 40 20. Georges Bank canyons 44 21. Two projected profiles of Georges Bank canyons 45 22. Geologic section at Cape Hatteras, Virginia 46 23. Correlation of structural benches off northeast United States 48 24. Geologic section: Western Europe based on refraction measurements 49 25. Index chart, location of abyssal hill profiles illustrated in Figures 26 and 27 62 26. Eleven profiles, Abyssal Hills Province, western Atlantic 62 27. Eight profiles, Abyssal Hills Province, eastern Atlantic 63 28. Tracing of PDR record, abyssal hills, southeast of Bermuda Rise 64 29. Northwest Atlantic Mid-Ocean Canyon 67 30. Eight east-west profiles showing Northwest Atlantic Mid-Ocean Canyon 68 31. Forty-eight cross sections of Northwest Atlantic Mid-Ocean Canyon 69 32. Long profile of Northwest Atlantic Mid-Ocean Canyon 70 33. Tracing of PDR record across Theta Gap 73 34. Natural scale profile, Kelvin Seamounts 77 35. Crustal sections in various physiographic provinces, determined by seismic-refraction measurements 81 36. Index to natural-scale Mid-Atlantic Ridge profiles reproduced in Figures 37-41 84 37. Natural-scale Mid-Atlantic Ridge profile 1A 85 38. Natural-scale Mid-Atlantic Ridge profile 1B 86 39. Natural-scale Mid-Atlantic Ridge profile 1C 87 40. Natural-scale Mid-Atlantic Ridge profile 2A 88 41. Natural-scale Mid-Atlantic Ridge profile 2B 89 42. Type profile, provinces of the Mid-Atlantic Ridge 90