50 



DISCOVERY REPORTS 



consisting of labradorite (somewhat albitized and epidotized), fresh pale augite with which the 

 feldspar laths are sometimes in ophitic relation, numerous brown pleochroic pseudomorphs after 

 hypersthene, and much diffused chloritic matter. There is also a micro-granular variant of this type 

 with porphyritic feldspars and hypersthene (bastite), and highly epidotized. An outcrop near the 

 glacier (Fig. 5) consists of pyroxene-andesite of a type common among the older lava series. It 

 shows porphyritic feldspars (andesine), pale brown augite, and chlorite pseudomorphs after ortho- 

 rhombic pyroxenes, in a very fine-grained intergranular ground-mass. The fourth specimen, from 

 the shore, is an igneous breccia mainly composed of angular fragments of altered andesite, much 

 epidotized, and peppered with cubes of secondary pyrites. Mr Ferguson's specimen of igneous 

 breccia from the same locality, however, is rich in fragments of the more acid dacitic and rhyolitic 

 lavas. 



COPPERMINE COVE , GnQLISM STRAiT, SOUTH SHETLAND: 



*i.tfV^ ->-"*j-L.-i:rta^ii 



STATION 14-85 



TABL€ I 



.CUM 







ii.JXJ^a4> 





X tnajiKd lEl tun«^j.t"iot^;ti^ CI ^jiuv^ ^<.Mo C«_ «^\ii.*. ahaUc. 





■DVKE 



^ ;^r1^f-?-^--rt-yi^?-rfT-^-.-y;^^Ty^^ 



Fig. 6. 



1^^ " 



ROBERTS ISLAND 



Coppermine Cove. This anchorage is situated at the north-western end of Roberts Island, close 

 to the multitude of small islands and rocks which are scattered over the northern exit of English 

 Strait. Specimens were collected by Dr Mackintosh from a small peninsula ending in a flat-topped 

 columnar rock known as Fort William (Fig. 6). Opposite the anchorage (reports Dr Mackintosh) 

 are cliffs of reddish breccia, presumably volcanic, and Fort William appears to consist of columnar 

 basalt. In this respect it resembles Table Island, and many, if not all, of the islets and rocks in the 

 vicinity. Many rock specimens were collected between the anchorage and Fort William. A dike 

 about 5 ft. thick cuts the cliff opposite the anchorage. 



The only previous description of rocks from Roberts Island is that by H. H. Thomas ((2), pp. 85-7). 

 He describes five specimens from Coppermine Cove, all porphyritic olivine-basalts and all showing 

 considerable variations in the relative abundance of the porphyritic constituents, and in the richness 

 of the ground-mass in ferromagnesian minerals. Most of Dr Mackintosh's specimens are also olivine- 

 basalts of varying composition and texture. Thus the columnar rock of Fort William is a feldspathic 

 olivine-basalt, or rather dolerite, with a ground-mass of excessively coarse intergranular texture 



