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Biostratigraphic data from the COST B‐2 well off New York and four deep commercial wells off Nova Scotia have been used to remove the effect of sediment loading at the Atlantic‐type continental margin off the East Coast, North America. The resulting subsidence contains terms due to both “tectonic” and “eustatic” effects. By assuming the tectonic subsidence is thermal in origin these effects can be separated. The “eustatic” effects have been isolated by least squares fitting an exponential curve to the subsidence data. The resulting sea‐level curve shows a maximum rise in sea‐level during the Late Cretaceous (about 75–80 m.y.B.P.) which probably does not exceed 150 meters. The tectonic subsidence has been interpreted in terms of a simple thermal model for the cooling lithosphere. Based on this model the thermal thickness of the lithosphere and the total amount of crustal thinning are estimated. These …