84 DISCOVERY REPORTS 



Gibbs Island is high and steep, rising abruptly out of the sea which is deep close inshore. The 

 coast almost wholly consists of sheer and inaccessible cliffs reaching a maximum elevation of about 

 I GOO ft. These rock walls are remarkably ice-free, and only a thin mantle of highland ice crowns the 

 rising ground above them. Gibbs Island is joined to Narrow Island by a low shingle and boulder 

 spit, 50-80 yards long, which is probably awash at high tide. In its general features Narrow Island 

 is similar to Gibbs Island. 



The south coast of Gibbs Island is largely composed of a fine-grained schistose rock penetrated 

 by occasional quartz veins. The planes of schistosity are conspicuous from the sea and dip south-west 

 at an angle of about 30°. Specimens of the rock were obtained from an outcrop near sea level on the 

 south coast near the landing place and from another outcrop about i ^o ft. higher. The steep screes 

 which descend to the sea are almost exclusively composed of slabs of the grey phyllite. Above the 

 screes, starting at 500 ft., is a vertical rock face reaching a height not far short of 1000 ft. As this 

 cliff has obviously provided the scree material it is undoubtedly composed of the same phyllite. About 

 100 ft. above the landing beach [in another direction?] is an outcrop of a massive, dark olive-green 

 rock [serpentine] which has given rise to boulders on the shore. 



GIBBS I. 



W.N.W. 



E.S.E. 



NARROW I. 



SCHIST DUN \TE;- SERPENTINE 



Fig. 12. 



Narrow Island, on its south side, appears from the sea to be composed of a massive rock of reddish 

 brown hue, with no sign of the schistosity which characterizes the southern face of Gibbs Island. 

 A landing was made on the south coast near the connecting spit, and a specimen was obtained from 

 the cliff face a few feet above sea level. This rock is the dunite-serpentine described below. 



From the data given above a tentative sketch section may be drawn showing the probable geological 

 structure of Gibbs Island (Fig. 12). The view is here taken that the serpentine has been intruded 

 parallel to the foliation planes of the schist. 



PETROGRAPHY 



The rocks of Gibbs and Narrow Islands comprise two sharply contrasted types, namely, schists 

 and serpentine. 



Schists. Five of the specimens were sliced for microscopic examination. They can be described in 

 general terms as chlorite-sericite-albite-schists containing, in addition, quartz, calcite, and minerals 

 of the epidote group (clinozoisite, zoisite) in some abundance. Small garnets and a mineral of the 

 chloritoid group are found in one specimen, and the latter mineral also occurs in another rock. In 

 hand specimens the rocks show a fine, parallel schistosity yielding flat cleavage surfaces varying in 

 colour from light silvery grey to lead grey. 



In thin section the rock containing garnet and chloritoid shows a thin foliation with somewhat 

 larger grains of quartz and feldspar taking part in a minute flaser structure. The garnets are small 

 and sparsely distributed; chloritoid is rather more abundant, and occurs as pleochroic grey-blue 

 prisms with good cross fracture. 



Another rock consists of a mosaic of small grains of quartz through which wind thin folia of 



