CHAPTER XIII 

 STRATIGRAPHICAL GEOLOGY 



Our ideas as to the general sequence of geological formations in the Ross region are 

 illustrated in Figs. 1, 2, and 3 of Plate LXXV. All three sections commence on 

 the inland ice, cross the great Antarctic Horst, and terminate in Ross Sea. As these 

 sections explain themselves, we may now pass on to consider in detail the different 

 formations represented. 



PRE-CAMBRIAN 



Rocks of the Pre-Cambrian age were traced at intervals by various members of 

 oxxv expedition from Cape Roberts near Granite Harbour, on the north, to possibly the 

 Beardmore Glacier, on the south. We say, " possibly," because some of the granites 

 of the Beardmore Glacier, though gneissic, may not necessarily be of Pre-Cambrian 

 age. The most typical exposure of what appeared to us to be Pre-Cambrian gneiss 

 in situ was that visited by the Northern Party at Cape Roberts, a few miles south 

 of the southern headland of Granite Harbour. In his notes on the Petrology of 

 South Victorian Land, at the end of this volume, Mawson states that he considers 

 that the gneiss of Cape Roberts closely resembles that of the South Neptune Islands 

 in South Australia. He states that this Antarctic gneiss contains frequent basic 

 schliers. These granite gneisses at Cape Roberts are traversed by dykes consisting 

 of coarse pegmatite at their margins, with fine aplite at the centre. The folia of 

 gneiss strike about N. 25° W., and dip about W. 25° S. at about 60°. On the 

 mainland, opposite Dunlop Island, at 17 miles south-west from Cape Roberts, there 

 is an outcrop of gneissic granite, the folia of which dip about north-west at approxi- 

 mately 30°. It is doubtful whether the whole of this rock can be considered true 

 gneiss. It has rather the appearance of belts of puckered gneiss caught up in a 

 grey gneissic granite. Amongst the erratics of Cape Royds were several of very 

 coarse gneiss and augen-gneiss rich in black mica. We did not discover this rock 

 in situ. Prior * describes a gneiss, closely allied to that of the rocks met with at 

 Cape Royds, as occurring in situ at the point marked D4 on Ferrar's geological 

 map in tlie Kukri Hills of the Ferrar Glacier Valley. He also describes the red 

 augen-gneiss from the Cathedral Rocks, and fi'om the same locality a hornblende 

 diorite. He adds that hornblende schists are associated with these gneisses. 

 * National Antarctic Expedition, vol. i., Geology, p. 125. 



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