About five miles from shore, the narrow crest of the ridge Is serrated by a series 

 of notches spaced at intervals of several hundred yards. These notches have a 

 maximum relief of 40 fathoms . The shallowest depths recorded on the ridge were 

 70 fathoms . These notches may have been cut by the roots of icebergs dragged 

 over the ridge by the three-knot ocean current . 



1 . North-South Transverse Ridge . The author suggests that the western shore 

 of Edward VII Peninsula and the tangential transverse ridge which extends north- 

 ward from Cape Colbeck describe a north-south line which, at least during certain 

 recurring stages of the Pleistocene, has marked the boundary between two distinct 

 glacial fjrovlnces . West of this border, in the Ross emboyment, was the province 

 of "wet-base" glaciers, while east of the border was the province of "dry-base" 

 glaciers. Carey and Ahmad (1961) define a wet-base glacier as one whose base 

 Is at melting temperature and therefore ha basal melt water; a dry-base glacier as 

 one whose base is below melting temperature. 



As an example of a dry-base glacier, Carey and Ahmad (1961) cite the Penchsokkia 

 Glacier (on the Atlantic coast of East Antarctica at approximately lO'W longitude) 

 and its floating ice shelf; the Ross Ice Shelf Is cited as an example of a wet-base 

 glacier. 



Where dry-base glaciers Impinge upon the sea, they have a sharp break in 

 surface slope at the line of buoyancy. At the grounding line, the thickness of the 

 floating side decreases abruptly by a factor of four to five. At this_ transition zone, 

 dry-base ice about 3,000 feet thick becomes buoyant in water 2,500 feet (420 

 fathoms) deep and thins rapidly to less than 600 feet leaving well over 300 fathoms 

 of open water beneath it, yet the 3,000-feet-thick grounded Ice is still resting 

 firmly on an only slightly shallower bottom (Corey and Ahmad, 1961; Robin, 1953). 



Wet-base glaciers show little or no surface indication of their grounding line. 

 As a wet-base glacier begins to float, it gradually thins and deposits till at its 

 base . The till still bears part of the weight of the glacier and is dragged or rolled 

 forward to be left where the water depth is just sufficient to give complete buoy- 

 ancy . Here a submarine slope develops at the angle of repose for the till . By the 

 time wet-base Ice reaches the Ice barrier where icebergs are calved, little sedi- 

 ment may be left In the Ice . The surface of the Ross Shelf is uniform for hundreds 

 of miles even though the shelf Is In many places "grounded" to within about seven 

 miles of the outer edge (Cbrey and Ahmad, 1961; Poulter, 1947). 



It Is now thought that the Ross shelf ice is not grounded over much of its area . 

 Where the ice does not touch bottom there is a distinct parallel between rises in 

 the sediment topography and rises In the ice bottom. Indicating that a layer of sea 

 water may be able to maintain its thickness despite movement of the Ice toward 

 shallower water (Zumberge and Swlthinbank, 1962; Crary, 1961). 



26 



