For example, on Operation HIGHJUMP during seven crossings 

 from the antarctic slope to the shelf, Dietz noted that the 

 break-in-slope depth varied from 230 to 280 fathoms. ' 



Extension of the bottom echo (fig. 3B), on both sides of 

 the break-in-slope, may show that steep slopes lie near to 

 and parallel with the ship's track and suggests that the outer 

 margin of the shelf may be furrowed. However, the passage 

 parallel with and close to the outer edge of the shelf (figs. 3B 

 and 3C) shows a smooth bottom between 60 and 70 fathoms in 

 depth so that even if canyons or furrows are present near the 

 break-in-slope, they do not deeply indent this shelf. 



After leaving the Pribilof Islands, the USS NEREUS pro- 

 ceeded northward to Bering Strait (figs. 3E, 3F, and 4A through 

 41). Except when stopped to occupy a station, the USS NEREUS 

 was continuously underway at about 13 knots, so that the 

 bottom profiles of figures 3, 4, 6, and 7 generally have a 

 vertical exaggeration of about 26 times. Considering such 

 a vertical exaggeration, the shelf along this track is remark- 

 ably smooth, being completely devoid of even minor irregu- 

 larities. For example, the gradient between stations 2 and 3 

 (figs. 3E and 3F) is 3 fathoms (18 feet) in 65 nautical miles, 

 or 0.28 feet per mile (1 in 17,000). Such an extremely low 

 gradient is of a magnitude more similar to that of a slow 

 flowing river than to that of even the flattest of land surfaces. 

 Thus, the Bering Sea has a surprisingly level bottom, which 

 is probably flatter than any other land surface of comparable 

 extent in the world. 



Along the track of the USS NEREUS, the bottom rises 

 gently and regularly to the north with an extremely low gra- 

 dient, reaching a minimum depth of about 21 fathoms, with 

 the exception of the track abeam of St. Lawrence Island, where 

 the depth is somewhat shallower. The smoothness of the 

 bottom makes it quite evident that this portion of the Bering 

 Sea was not glaciated during the Pleistocene. However, even 

 the conservative estimate of from 57 to 66 fathoms as the 

 maximum Pleistocene sea level lowering" indicates that a 

 large portion of the Bering Sea must have been dry land. 

 Yet, there are no minor irregularities on the shelf that might 

 be interpreted as wave-cut terraces, stream valleys, or 

 ancient strand lines. It is, therefore, quite probable that 

 there has been sufficient recent sedimentation, plus some 

 wave-cutting on the shelf, to cover and mask any minor topog- 

 raphical irregularities produced during the Pleistocene lower 

 stands of sea level. The relatively shoal depth of the Bering 

 Sea shelf, as compared to shelves in other parts of the world, 



