============================================================================= |St. | |Charles-| | |Bar |St. | | Placentia|John's,|Norfolk,|ton, |Bimini,|Miami,|bados,|Vincent,|Dakar|Dakar Bay, Nfd.|Nfd. |Va. |S. C. |B.W.I. |Fla. |B.W.I.|C.V.I. |North|South ============================================================================= 10 12 10 8 10 8 10 15 15 15 20 18 20 20 18 20 20 25 24 30 30 28 30 28 28 35 38 35 35 32 40 38 38 38 42 45 42 45 42 45 50 50 55 55 58 56 54 55 55 68 65 68 65 60 72 76 72 80 80 80 80 85 81 80 78 ----------------------------------------------------------------------------- CONTINENTAL MARGIN BENCHES: On each profile across the continental margin is a series of benches and changes in gradient which range from the shelf break to slight changes in gradient on the continental slope. If a field geologist enters a new area of sedimentary rocks where road cuts do not exist he invariably goes to the stream valleys, and here he gets his first and best view of the geologic section. The stream's gradient is adjusted to the resistance of the rocks over which it cuts, and the form of the valley-side slopes reveals the nature of the underlying rocks even if they are grassed over. This obvious field method had never been fully applied to the continental margin. Stetson (1936) dredged in the canyons of Georges Bank, and his hauls included Cretaceous sandstones and Tertiary marls and green sands. He concluded that the canyons had been cut deep into the continental margin to expose the underlying Cretaceous rocks, but he considered the continental slope the product of depositional processes. However Upham (1894) had suggested that the continental slope formed a continuous outcrop of Tertiary and Cretaceous sediments from Newfoundland to Florida, a suggestion the writers consider quite probable. That is to say, an analogy can be made between the continental slope and one face of the Grand Canyon or to an erosional escarpment bounding a high mesa or plateau like the Book Cliffs of Utah and Colorado.