146 AUSTRALASIAN ANTARCTIC EXPEDITION. 



(Plate XXIX.). The general outline suggests ice cap erosion, but real smoothing 

 is only seen up to 30ft. or 40ft. above sea level. At higher levels loose blocks 

 are scattered about in a manner that indicates no ice sheet has recently passed over the 

 island. No undisputed erratics are found, though several blocks illustrate a phase of 

 the local gneiss not observed in situ in the island. Some very large blocks were noted 

 removed short distances from their original position to situations where gravity could 

 not possibly place them. 



If the snow banks and ice foot were completely melted, the present island would 

 probably be intersected by one or more sea-water channels. These channels are at the 

 present time bridged by ice and undermined by the sea, and caverns are produced with 

 rock walls and ice roofs. These breaks are in an approximate east and west direction, 

 and remind one of cross-channel structure of the Mackellar Islets. They may 

 correspond with the sea-water channel that divides the two portions of the Cape Pigeon 

 Rocks. 



The most conspicuous rock is a massive, light-coloured granitoid gneiss, often 

 carrying abundant dark aggregates of garnet and mica, which are more or less spherical 

 in shape and from |in. to 2in. in diameter. Varieties of gneiss are also found without 

 any garnet at all, and the highest part of the island is formed of an acid hypersthene 

 gneiss. In crossing the islet areas are found consisting of more strongly foliated gneisses, 

 and the trend of the foliation is a little west and north. Irregular bands of black gneiss, 

 with dyke form, exist here as at Cape Denison, and some of them are full of fine garnet. 



THE GARNET GNEISSES. 



In the various outcrops the garnet gneiss exhibits foliation whose general trend 

 is a few degrees west of north. Both Garnet Point and Stillwell Island are noted for 

 the large garnet-mica aggregates which are relics of former complete garnet crystals. 



Cape Gray. 



At Cape Gray there is a rather coarse-grained rock (No. 784) which has a banded 

 character in the hand specimen. It contains light-coloured bands of coarse felspar 

 and garnet, appearing through a darker mass containing mica and garnet. The bands 

 are irregular, being both thick and thin. 



In the slide the rock is heteroblastic and the garnet crystals are much larger than 

 the other constituent minerals. In part the quartz and felspar form granoblastic 

 aggregates in which cataclasis is absent and diablastic structure is not common. The 

 fresh character of this quartz and felspar appears in contrast to the finely granulitic 

 character of the cordierite. The felspar is chiefly orthoclase and perthite. Microcline 

 and some lamellar twinned sodic plagioclase are also present. The garnet is pink in the 

 hand specimen and almost colourless in the section. It appears in small crystals as 

 well as the large individuals, and usually has an irregular outline. There is a tendency 



