GRANITE HARBOUR 81 



At Gregory Point it terminates against the area glaciated by the Mackay 

 Glacier and the Bonney Valley and Glacier. 



Next, at 15 miles south of Depot Island, we reach Gi'anite Harbour, a magni- 

 ficent inlet, with the Mackay Glacier at its head. This glacier lies in a very typical 

 over-deepened valley, with a far wider valley above, lying at a height of about 1500 

 feet above the present surface of the ice of the Mackay Glacier. The sketches * 

 speak for themselves as to this evidence, and better testimony is borne by the 

 excellent photographs of the Discovery Expedition (National Antarctic Expe- 

 dition, 1901-4, Plate XXXVI. Figs. 1, 2, and 3). Figure 3 particularly shows 

 extremely well the great terrace of the wide original valley above the over- 

 deepened valley, with the strongly facetted hills rising above this upper terrace. 

 The spectacle afforded by the Granite Harbour is truly magnificent, and most 

 impressive and interesting for students of ice and its work. The sheer glacier- 

 cut walls on the north side of the Mackay Glacier and Granite Harbour, and the 

 steep slopes of the rocks boimding the over-deepened valley on the south, show that 

 the present glacier must extend much below sea-level. 



As no complete set of soundings f were obtained at the head of the bay in whicli 

 the glacier lies, it is impossible to form more than a rough guess at this thickness, 

 but the angle of slope of the rocks on either side of the valley and the height of the 

 ice cliff at its seaward end being taken as some criterion , it is probably of the order of 

 somewhere about 1000 feet. Ice-falls were conspicuous, crossing the valley just below 

 the remarkable line of nunataks. The wonderful nunatak, Suess Nunatak, shows, 

 as seen in the sketches, two vast glacier-scooped concave surfaces respectively on 

 its northern and southern sides, and a conspicuous hollow occupied by a small snow- 

 field at its summit. Suess Nunatak could be seen to be formed of some black rock, 

 probably part of a dolerite sill. Higher up the valley, to the right, stratified rocks, 

 evidently of the Beacon Sandstone formation, make their appearance, traversed by 

 dark dykes and sills. The cross section of this remarkable valley, based on Mawson's 

 theodolite determinations from distances which varied from 5 to 10 miles, is showii 

 in Fig. 40. 



The following three sketches were made successively from north to south, the 

 uppermost sketch representing the northernmost view. 



There can be little doubt that the ancestor of the Mackay Glacier during the 

 maximum e-laciation had a cross section at least six or seven times the area of the 

 present glacier. 



Without discussing the whole question of over-deepened valleys here, or the 

 origin of the great upper terrace, it may be remarked that so far as the area 



* The focal plane of our camera refusing to work in the great cold at the time of our visit in 

 October, we had to rely on sketches only. 



j H. T. Ferrar states, in Nat. Ant. Ex. Natural History, vol. i., Geology, p. 94, " This harbour 

 is fiord like, and has depths of over 100 fathoms within a quarter of a mile of the shore." 



