312 AUSTRALASIAN ANTARCTIC EXPEDITION, 



The minerals present in these two rocks are much alike. The dominant one is a 

 pale blue-green actinolite. This is sometimes concentrated in zones free from other 

 minerals, and sometimes associated with highly saussuritised felspar. The saussuritic 

 mass contains epidote, zoisite and clino-zoisite. No. 632 contains an occasional lath 

 of biotite, but this mica, as an unusually pale variety, is one of the determinative 

 minerals of the finer-grained regions of No. 633. Each rock contains some granules of 

 sphene, rare grains of ilmenite and crystals of apatite. 



No. 635A is a rock in which the simpler pale-green actinolite has been recrystallised 

 into more complex green amphibole. This recrystallisation of amphibole has been 

 accompanied (or preceeded) by a recrystallisation of felspar. The hornblende crystals 

 are small, but no longer exclusively elongated, as a matter of fact they are usually 

 equi-dimensional. They do not exhibit such marked parallelism as do the crystals of 

 amphibole in No. 633. Sphene has practically disappeared, the biotite has a much 

 stronger reddish brown colour. These facts, together with the deeper green colour of the 

 amphibole, again emphasise the way in which the amphibole (and the mica too) gain 

 complexity in the higher grades of metamorphism by the absorption of the " rejection 

 products " of saussuritisation and of minerals like sphene. Lawsonite and the suite of 

 epidote minerals are practically absent. 



The recrystallisation of the felspar has resulted in the formation of many grains 

 of quartz. The new felspar is frequently twinned, both albite and pericline multiple 

 twin lamellae being seen. 



Some little iron ore (magnetite) and rods and needles of apatite are also present. 



These three rock types can be summarised thus : 

 No. 632 Chlorite-albite-epidote-amphibolite. 



No. 633 Chlorite-albite-epidote-amphibolite-schist. 

 No. 635A Amphibolite. 



II. NOTES ON ADDITIONAL ROCK TYPES FROM STILLWELL ISLAND. 



1. INTRODUCTION. 



A discussion of some of the rock types found at Stillwell Island has already been 

 given in these Scientific Reports (Stillwell, Vol. Ill, Pt. 1). A brief resume of some of 

 the points made there is necessary for an understanding of the sequel. 



" Stillwell Island is one of the largest members of the Way Archipelago. 



The most conspicuous rock is a massive granitoid gneiss, often carrying abundant 

 dark aggregates of garnet and mica. Varieties of gneiss are also found without any 

 garnet at all, and the higher part of the island is formed of an acid hypersthene gneiss. 



