266 AUSTRALASIAN ANTARCTIC EXPEDITION. 



in situ at Cape Denison 1 . Apart from the porphyroblastic character the rock is a 

 typical amphibolite, with dominating hornblende and very little brown biotite. The 

 felspar is clear andesine with indefinite and intermittent twinning. 



A schistose variety is represented by No. 597, in which the light-coloured 

 constituents are sufficient to produce a greyish colour in contrast to the black colour 

 of the normal amphibolite. Tt is a biotite-amphibolite-schist, carrying lawsonite, 

 epidote, and coarse crystals of apatite. The epidote and lawsonite are interlaminated 

 with biotite, and the development of these minerals indicate an approach to the Epi 

 division of this group. 



EPI DIVISION. 



Specimen No. 985 is a jet black schistose chlorite-amphibolite, similar in most 

 respects to the preceding variety, No. 597. The biotite of No. 597 has been mostly 

 converted into chlorite in No. 985, and most of its felspar has been saussuritised. These 

 changes are considered to be Epi features, superimposed upon a typical amphibolite. 

 Large vein-like segregations of saussurite are present in the hand specimen of No. 985. 



Another chlorite-amphibolite is specimen No. 520. Biotite is completely replaced 

 by chlorite, and the alteration is accompanied by the separation of a little quartz. An 

 interesting feature in this case is the separation of the blue glaucophane constituent 

 from the complex molecule in a manner similar to the schiller inclusions that are 

 sometimes found in hypersthene. The result is a mottled green and blue crystal of 

 hornblende (PI. XL. fig. 1). Apatite and ilmenite are abundant minor constituents, 

 and most of the felspar is cloudy and saussuritised except for small areas of clear 

 albite. 



The same mottling of blue and green hornblende is developed in a lesser degree 

 in the amphibolite No. 965. This specimen possesses a pronounced " sieve " structure, 

 in which the hornblende is highly perforated with colourless inclusions. The plagioclase 

 is cloudy. Some of it possesses prominent diablastic structure, representing one stage 

 of its development, but most of it forms a fine granulitic aggregate of acid plagioclase. 

 Crystals of apatite and ilmenite are large and unusually abundant. A little chlorite 

 is present, derived from biotite, and pyrite is also present. 



Another variety of chlorite-amphibolite is No. 247. This specimen is a schistose 

 rock, in which abundant lenticles or porphyroblasts of felspar are set in a dark matrix 

 of hornblende, mica, and felspar. The base of the rock is similar to the biotite- 

 amphibolites, except that biotite is replaced by chlorite. In this and the preceding 

 examples the chloritisation does not extend to the hornblende. Quartz is present 

 showing cataclasis, and, together with the abundant felspar, indicates a gradation 

 towards the more acid group of the plagioclase gneisses. Some of the felspar lenticles 

 consist of large saussuritised plagioclase, partly surrounded by clear, recrystallised 

 felspar. Others consist of granoblastic masses of andesine felspar, with a little quartz. 



1 Op. cit, p. 48. 



