[Illustration: FIGURE 13.--_Eastern Channel, Gulf of Maine_ Profile replotted from NMC echogram] Laurentian Channel.--Between Nova Scotia and Newfoundland a 60-mile-wide, steep-sided, flat-floored channel cuts across the continental shelf connecting the Gulf of St. Lawrence and the open ocean. The nearly flat, smooth floor of this channel lies at about 230 fathoms depth. Figure 12 shows a cross-section of the Laurentian Channel near its seaward end. The origin and physiography of the channel has been treated by Shepard (1931; 1948); its structure has been reported by Press and Beckmann (1954). The Laurentian Channel continues as a steep-sided, box-shaped feature for more than 500 miles into the Gulf of St. Lawrence. Scotian Shelf Sector.--The term Scotian Shelf was introduced by Canadian oceanographers and refers to the continental shelf southeast of Nova Scotia from the Laurentian Channel to the Gulf of Maine. This region is illustrated by Profiles W-7, W-8, W-9, W-10, and W-11 which run at slightly different directions, all starting in the vicinity of Halifax, Nova Scotia. Along the entire Scotian Shelf a series of 120-fathom depressions are located 10 to 80 miles off shore. A nearly continuous bank 20-60 fathoms deep and 10-25 miles wide lies along the seaward edge of the Scotian Shelf. From northeast to southwest this feature is divided by low saddles into Banquereau Bank (20-40 fathoms), Sable Island Bank (0-20 fathoms), Emerald Bank (40-60 fathoms), Lahave Bank (50-60 fathoms), and Browns Bank (20-60 fathoms). These shelf-edge banks culminate in the low, sandy Sable Island which stretches for about 25 miles along the outer edge of the shelf. In profile W-7 the break from the nearly flat shelf to a gradient of 1:50 occurs at 50 fathoms; a second break occurs at 80 fathoms. A gradient of 1:10 is reached at the 150-fathom curve. Profile W-11 is somewhat similar to W-7 in the form of the shelf break. Profiles W-8, W-9, and W-10 show shelf breaks at 50, 60, and 70 fathoms respectively.