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Gravity sections are presented for 10 profiles off the east coast of North America. The gravity effects for the upper sedimentary layers and the basement rocks, observed by seismic refraction measurements, are computed and subtracted from the gravity sections. The residual anomalies are attributed to fluctuations of the mantle surface. The shape of this surface which accounts for this residual anomaly is computed. The transition from a continental type crust to an oceanic type crust occurs fairly abruptly within a distance of about 200 km. The true continental edge is located at about the 1,000-fathom depth curve in the ocean.
Sections across continental margins of the west coast of Central America, the west coast of Chile, and the west coasts of Europe and Africa are compared with those of the east coast of the United States. Though differing considerably in details, the main features are somewhat similar.
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