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During the last 20 years extensive geophysical investigations have been carried out on the emerged and submerged Atlantic coastal plain of the United States. These include over 300 seismic refraction profiles, numerous gravity measurements from both submarines and surface vessels and total intensity magnetic measurements from ships and aircraft.
The geological structure of the area between Newfoundland and Cape Hatteras has been determined in some detail by these measurements. The predominant features are two linear troughs paralleling the edge of the continental shelf and separated by a ridge in the basement. The shelf trough contains up to 18,000 feet of sedimentary material while the outer one contains in excess of 25,000 feet in places.
Comparisons of this structure with the Appalachian Mountain system taken as a whole reveal many interesting parallels. Prior to the Taconic orogeny the Appalachians must have resembled the present continental margin in general characteristics.
The picture south of Cape Hatteras is not as clear. The structure is more complicated and the refraction results are more difficult to interpret due to the presence of calcareous sediments. The Cape Fear arch appears to be the dividing line between the two structural types.
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