The sand tends to be smooth, hard, and flat with a variety of surface bedforms. Both types of bottom are classified as Sable Island Sand and Gravel. The margins of Outer Shelf Banks deeper than 110 m have sediments that are principally sand and contain small amounts of clay, silt, and frequently gravel. The surface may be flat and smooth to undulating and hummocky. Called Sambro Sand, these deposits cover the saddles adjacent to the Outer Shelf Banks in many cases.
Tidal action tends to produce a mixed water column on banks.
The water column on the shallower banks may be well mixed through much of the year, while the deeper banks have a stratified water column. It is in these areas that shelf-break mixing processes occur. The biomass of phytoplankton, the productivity, and the seasonal pattern of the waters over the shelves are similar to those found between the banks. Thus there is no greater food supply for other organisms here than over adjacent banks and saddles. The outer edges of the banks are an exception, as phytoplankton productivity is greater in the zone of interaction of shelf and slope waters.