In the left margin of the Gulf Stream, looking in the direction of flow, a narrow discontinuous band of relatively cold water is often found. This haa been attributed to upwelling from the colder depths of the ocean, but recent investigations throw doubt on this explanation, since this water, which forms a thin layer close to the surface, may have a lower salinity than any water in the depths. Evidence is given that the only cold low salinity source is the so-called Shelf water, which is found in a broad band between· the shore and a boundary off the Continental Shelf....