The foraminiferal fauna in more than 35 submarine cores, collected by H. C. Stetson from the continental slope of the western North Atlantic, have been examined to determine the areal and vertical extent of present and previous assemblages. Below the present fauna, recorded at the top of the cores, there is a widely distributed fauna of Arctic to sub-Arctic aspect not now living in this area. This fauna is similar to the one reported from the Georges Bank canyons and from a core in this area, and is identified by Cushman as Pleistocene. This Pleistocene fauna is probably of Wisconsin age, since it lies directly beneath the present fauna. At the western edge of the basin of the North Atlantic ocean, beyond the continental slope, two Arctic faunas have been recognized below the Recent assemblage and are separated by a pelagic warm-water fauna typical of the present Gulf Stream region. This may represent two Pleistocene stages or it may indicate separate maxima of the last stage.
In a few cores a foraminiferal fauna is recorded a short distance beneath the surface in which pelagic types characteristic of warm surface water are considerably more abundant than in the present-day assemblage. This suggests a possibility of a postglacial shift in warm surface water areas.
New information concerning distribution suggests that water temperature may be the most important regulating factor in the occurrence of many Foraminifera.