GRANITE AND ASSOCIATED DYKE-ROCKS 245 



I. GRANITE AND ASSOCIATED DYKE-ROCKS 



1. The Granites. These comprise grey granites containing little or no horn- 

 blende, with biotite, zircon, and allanite. The granite of Cape Irizar and Mount 

 Larsen may be taken as typical of this variety. This granite is distinctly alkaline. 

 The fact that pink felspar is absent from the arkoses of the Beardmore Glacier leads 

 Mawson to the conclusion that these grey granites, which are represented in the 

 arkose, are older than the pink granites. 



In the neighbourhood of the Beardmore Glacier is a coarsely crystalline por- 

 phyritic grey granite apparently allied to the Cape Irizar and Mount Larsen 

 types. 



Quite distinct from the grey granites, and obviously newer, are the pink granites. 

 Ferrar considered that these pink granites intrude the dolerite sills which have 

 burst their way through the Beacon Sandstone. If this view is correct the dolerite 

 is Post-Gondwana, and the pink granite still later in geological age. We were un- 

 able to see the spot where Ferrar believed that there was evidence of the intrusion 

 of the pink granite into the dolerite. So far as our observations extended, it seemed 

 to us that the pink granite was on the whole older than the dolerite, and we pro- 

 pose provisionally to class it as such, without of course intending to exclude the 

 possibility that there may be a later local development of pink granite which may 

 intrude the dolerite. For the petrological details of these rocks readers are referred 

 to the chapters by Dr. Mawson and Professor Woolnough at the end of this work. 

 We are specially concerned with their field relations. 



In the lower diagram of Plate XCIL, Chapter XX., an attempt has been made 

 to show the relations of these rocks to one another in chronological order. 



The order seems to be as follows : — 



la. Diorites. At the southern slope of Mount Crummer fine examples were 

 observed of a greyish granite intruding masses of dark dioritic rock. 



It was very obvious that the granite rock was the newer. There is, therefore, 

 clear evidence here of a sequence from older basic rocks into newer acid types. It 

 is not possible to separate these in geological time from the diorites. The locality 

 where the junction was sketched is Camp Lake, at the foot of Mount Crummer. 

 Mawson suggests that the characteristics of the diorite rocks are not typical of 

 normal diorites, but are suggestive of lamprophyric separations. In his comparative 

 analysis he places side by side the diorite from CamjD Lake, that from the Moraine 

 about 20 miles south-east of Mount Larsen, and that from Cathedral Rocks, Ferrar 

 Glacier, together with a kersantite intersecting the pink granite at Cape Irizar. 

 Obviously in geological time the last-mentioned rock is much newer than the diorites 

 of Camp Lake. 



\b. Gabhros. These were not met with in situ, but being often sphene-bearing, 



appear to be closely related to the sphene-diorites included in the sub-gneissic 



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