The continental rise off the east coast of North America is a broad sedimentary apron 200-500 km wide, 1,200-5,200 m below sea level, with an average gradient of less than 1°. Continuous seismic-profiler recordings indicate that the rise is a prism of sediments lying on a strong and nearly level reflecting layer known as Horizon A. This horizon is believed to be the top of a turbidite sequence delineating an abyssal plain that covered most of the North American basin near the end of the Cretaceous Period. Progradation

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of the overlying Cenozoic sediments of the continental rise has decreased the width of this Cretaceous abyssal plain by as much as 200 km.

Sediments of the continental rise range in thickness from about 3 km at the base of the continental slope to several hundred meters along the seaward edge of the rise where it joins abyssal plains. Through most of its length the sedimentary sequence is separated from the continental slope by an unconformity. Seismic-profiler data reveal many examples of deformation within the rise due to slumping and gravitational sliding. The lower continental rise hills located at or near the rise-abyssal plain contact probably are the toes of these structures.

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