SUMMARY OF THE DISTRICT 115 



feet, while in Mount Lister the horst culminates in a peak nearly 13,000 feet high. 

 This peak is only an elevated horn on a plain, the level of which ranges from 11,000 

 up to nearly 13,000 feet. Towards the seaward ends of East Fork and Dry Valley 

 there is a remarkably deep notch in the coast-line. This is known as New Harbour, 

 and measures 10 miles wide by about 8 miles. One cannot but infer that this 

 remarkable inlet is due to the prolonged excavating action of the two most energetic 

 branches of the Ferrar Glacier, as it was when the ice flood was at its maximum, 

 viz. East Fork and North Fork. The inlet is in every way comparable with that 

 of Granite Harbour, but is on a somewhat larger scale. As already stated, the Dis- 

 covery Expedition obtained soundings of over 100 fathoms within a quarter of a mile 

 of the coast of Granite Harbour, which suggest that this harbour is a deeply eroded 

 glacial fiord. Unfortunately no soundings, as far as we are aware, have as yet been 

 obtained at New Harbour. Unless the wide fiord has been largely filled in with 

 moraine material by the retreating bi-anches of the Ferrar Glacier, there can be 

 little doubt that deep soundings should be obtained close inshore here, as at Granite 

 Harbour. 



Soundings obtained by Captain F. P. Evans of the Nimrod show that to the north 

 of Granite Harbour, at 6 to 8 miles from the land, the depth of the sea ranges from 

 360 fathoms up to 462 fathoms. His soundings between Cape Bird and Cape Royds 

 show that there is a uniform depth of from 460 to 470 fathoms along the east side 

 of McMurdo Sound at only 4 miles off" the land. The few soundings which he 

 obtained midway between Granite Harbour and Cape Bird prove the existence of 

 a remarkable submarine ridge. Tlie depth of water over this ranges from about 

 110 fathoms to 170 fathoms. 



Three possible explanations suggest themselves to account for this -submarine 

 ridge : — 



1. That it is a tectonic ridge due to the upward warping of the sunken 

 segment. 



2. The sunken segment between Boss Island and the mainland in this region 

 may not have been warped, but may have been originally flat. The depth of 110 

 fathoms may represent the approximate amount to which this segment was depressed 

 below sea-level originally, and the depth in excess of those met with in the soundings 

 near Granite Harbour and along the west coast of Boss Island may be due to the 

 increased erosive force of the McMurdo Sound portion of the Boss Barrier whei'e it 

 received the extra loads and pressures from the glaciers of the mainland on its west 

 margin, and those of Mount Erebus on its eastern side. 



3. It is possible that the maximum depth recorded, such as 472 fathoms near Cape 

 Bird, approximately represents the depths to which the sunken segment of McMurdo 

 Sound originally descended, and the shallower central portion may represent a vast 

 amount of moraine material which has been transported on the Boss Barrier from the 

 south carried from the direction of Minna Bluff, Mount Discovery, and Mount Morning, 



