388 DISCOVERY REPORTS 



are white granular rocks built up essentially of calcite showing abundant secondary 

 twinning. The shearing which these rocks have suffered has led not only to a marked 

 development of mechanical twinning but also to bending of the lamellae. Granulitiza- 

 tion is evident in some of them, larger grains of calcite being surrounded by a granu- 

 litized matrix of smaller grains. Accessory minerals are scarce and are represented by 

 muscovite and epidote. 



One specimen is of particular interest as providing a link between the marbles and the 

 hornblendic rocks next to be described. It is a banded rock, bands of marble inter- 

 digitating with darker bands rich in biotite and hornblende. The purer carbonate band 

 is built up of calcite, epidote, garnet and a little sphene, while the darker band is formed 

 of hornblende, biotite and clear albite. 



II. Garnet hornblende schists. These are coarse-grained rocks in which hornblende 

 or hornblende and garnet are conspicuous. The black hornblendes occur in elongate 

 crystals reaching up to 2 in. in length and the garnets reach half an inch in diameter. 

 These are set in a white siliceous or felspathic ground-mass. The elongated hornblende 

 crystals lie characteristically criss-cross in the schistosity planes. 



Under the microscope the constituents observed are garnet, green hornblende, 

 epidote, quartz, albite, variable amounts of biotite and muscovite, calcite and accessories, 

 apatite, sphene and ilmenite. 



Some of these examples contain considerable amounts of albite. There can be no 

 doubt that the rocks are genuine metamorphosed sediments of the character of meta- 

 morphosed shaly limestones or marls linked to the marbles by the presence of epidote and 

 calcite. Hand specimens have a striking resemblance to the \Nt\\-k.no^NnGarbenschiefer 

 of the Tremola series of the St Gotthard. 



Rocks of this type have been collected from the eastern side of the island (by the 

 graveyard) and in association with marbles at 400 ft. (see map). 



III. Garnet hornblende biotite schist. Rocks of this type come from Borge Bay. They 

 contain conspicuous garnets up to i in. in diameter and differ from the rocks of group II 

 chiefly in their richness in biotite. In addition they contain some muscovite, quartz and 

 acid plagioclase. 



IV. Garnet mica schists. These rocks are reported as forming the chief rock types of 

 the island. They consist of a series of foliated quartzose mica schists much veined with 

 quartz. Many are garnet bearing and all contain biotite. Oligoclase and albite figure as 

 constituents of the quartzose matrix. 



Station 1093: Coronation Island (Useless Bay) 



This collecting point is situated on the south coast of Coronation Island immediately 

 north of Signy Island, on Normanna Strait. 



The rocks collected iti situ are quartzose muscovite biotite schists much veined by 

 quartz and are identical with the rocks of group IV from Signy Island (St. 1092). 



Two rocks recorded as boulders are altered dolerites with pseudomorphs of bastite 

 after hypersthene and appear to be erratics. No rocks of this character have been 

 recorded in place. 



