The distribution of sediment on the crest mountains and high fractured plateau of the Mid-Atlantic Ridge at 45° N has been studied by seismic profiling. Sediment is ponded in intermontane valleys within the crest mountains and the plateau. It is also draped over the highlands of the plateau. Mean sediment thickness increases with distance from the valley out to 160 km, the limit of the study. The sediment data is not conclusive with regard to a break or change in the rate of the ocean-floor spreading between 8 and 10 m.y. ago in this area. Rates of sedimentation have been a few cm/1000 y during the past few m.y. It may have been more rapid in the past 100 000 y.