As the trend of the longitudinal depressions is at right angles to the general 

 direction of movement of continental ice, such depressions probably mark the 

 position of one of the following: 



a . a zone of less resistance to ice erosion caused by either: 



1 . a major fault zone with downdrop of the outer shelf relative to the 

 inner shelf during the Tertiary or during the Quaternary or 



2. a distinct lithology change, the inner wall of the longitudinal de- 

 pression representing the bedrock surface where it plunges beneath the 

 softer, more recent sediments of the outer shelf. 



b . a narrow rift zone of 



1 . a graben or 



2 . the steep downbending of the crust along one side of a fault . 



It is the writer's opinion that geophysical measurements will be needed to 

 determine the structural significance of the longitudinal depressions . 



It appears that Quaternary glacial action has at least aided in keeping these 

 great depressions open, regardless of their structural origin . 



C . Longitudinal Ridges 



The pauses in the Holocene transgression noted by Curray (1961) and others 

 may show their reflections on the Antarctic continental shelf in the form of end 

 moraines. Pennel Bank at the entrance of the Ross Sea and Mawson and Davis Banks 

 off East Antarctica have been interpreted as morainal (Taylor, 1930; Roos, 1937; 

 Fairbridge, 1952; Voronov, 1960; Zhivago, 1962) . 



The terminal moraines of the ice sheet at its maximum extent were probably 

 shoved over the shelf edge onto the continental slope . In this way, the continental 

 shelf may have been somewhat widened during the Pleistocene. 



The longitudinal depression off the north shore of Edward VII Peninsula is rim- 

 med on its outer edge by a longitudinal ridge. The crest of this ridge is approxi- 

 mately 20 miles offshore and lies about midway between shore and the outer edge 

 of the continental shelf. The longitudinal ridge has a gently rounded, irregular 

 surface with a relief of 100 to 200 fathoms above the outer shelf surface . The 

 shoalest sounding, 110 fathoms, was found near the inner edge of the ridge, only 

 five miles from the bottom of the longitudinal depression . 



To the northeast, on the opposite side of the transverse depression, is another 

 longitudinal ridge . On the southwest shoulder of this ridge, a core sample was 



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