PRE-CAMBRIAN 233 



Mawson records the occurrence of an erratic block of granite at Cape Irizar 

 weighing several tons. This shows well the early stages of gneissification. He 

 says, " The felspars usually show crush only round the edges. It contains, besides 

 the usual constituents, a little grey sphene, pleochroic yellow-brown allanite, and 

 small apatite prisms." He also notes that a gneissic granite occurs in situ at a 

 rocky point about 8 miles south of Cape Irizar. Amongst the accessory minerals 

 he notes several grains of faintly coloured fluorspar. It seems doubtful to us 

 whether either of these two specimens belong to Pre-Cambrian time, though it is 

 possible that they may do so. On the other hand, there can be little doubt that 

 the erratics collected by one of us (Priestley) at Dry Valley, and described by 

 Mawson respectively as banded gneiss and mica schist with large poikiloblastic 

 felspars from Dry Valley, and a sphene-bearing actinolite-gneiss from the upper 

 glacial moraine of the Ferrar Glacier, are really of Pre-Cambrian age. 



It is clear from these observations, combined with those of our party at Cape 

 Roberts, that there is a great development of gneissic rocks, apparently Archaean, 

 extending at any rate from the Ferrar Glacier Valley to Granite Harbour, a distance 

 of over 50 miles. At Marble Point, about 16 miles south of Dunlop Island, there is 

 a fine outcrop, on the coast, of very ancient metamorphic rocks, and these consist of 

 amphibolite rock with large hornblendes up to as much as 3 inches in length, the 

 general grain size being about half an inch. Calc schists and much contorted mica 

 schist are associated together with granite and aplite. We saw no evidence of any 

 massively intrusive granite there. The trend of the chief lines of folding in this 

 metamorphic series was about N.N.W. 



At Cape Bernacchi, about 5 miles south of Marble Point, there is a fine outcrop 

 of what appear to be Pre-Cambrian crystalline rocks. The most conspicuous member 

 of this group is coarse-grained saccharoidal marble containing flakes of graphite. It 

 contains also iron pyrites, copper pyrites, reddish biotite, garnet and epidote. It is 

 associated with tourmaline schists, and much epidote also occurs in bands as well as 

 a mica granulite, pyrite- and epldote-bearing quartz veins, and irregular patches, a 

 few feet in diameter, of coarse biotite-bronzite rock. The reddish-brown biotite of 

 the Marble Point series was found by Mawson to contain a notable percentage of 

 manganese. This belt, extending from Cape Bernacchi to Marble Point, is most 

 promising for the occurrence of economic minerals. The following sketch illustrates 

 the mode of occurrence of this series at Cape Bernacchi. 



The folia at Cape Bernacchi are much contorted ; at the extreme point it was 

 observed that they dip north at about 15 degrees. Several fragments of similar 

 marble were collected at the Stranded Moraines. These also are graphitic, and 

 contain small quantities of quartz, apatite, iron pyrites, and copper pyrites. In the 

 moraines of Dry Valley several fragments of schist and gneiss were collected. In 

 Mawson's opinion, they seem to have originated from the alteration of calcareous 

 slates and sandstones. The erratics of scapolite-bearing gi^anulite, described at the 



