86 



DISCOVERY REPORTS 



however, the crystals have been ground to powder, and wind in streaks around larger fragments which 

 have assumed a pseudo-spherulitic form. 



The dunite-serpentine of Narrow Island has been analysed by F. Herdsman, A.R.S.M., with the 

 results shown in Table 5, col. i. For comparison an analysis of dunite-serpentine from Cornwall is 

 given. The resemblance between the two analyses is obviously very close. The calculated norms of 

 both rocks give about 50 per cent olivine and 40 per cent enstatite. While the Cornish rock is stated 

 to contain some enstatite and tremolite {op. cit. p. 64) not a trace of these minerals can be found in 

 the dunite-serpentine of Narrow Island. It may perhaps be surmised that in the alteration to serpentine 

 there has been some differential abstraction of magnesia and iron oxide relative to silica. This appears 

 to be the first record of dunite and serpentine in the West Antarctic region. 



Table 5 



CHEMICAL COMPOSITION AND ORIGIN OF THE METAMORPHIC 

 ROCKS OF THE ELEPHANT AND CLARENCE GROUP 



No new analyses have been made of the rocks described above, since none of them has been collected 

 in situ or located with exactitude except a few from Gibbs Island. Four analyses, however, have been 

 published, two each from Elephant and Clarence Islands, and these are collected in Table 6, together 

 with a few comparable analyses from Tierra del Fuego, South Georgia, etc. 



Prof. Tilley regards the rocks of Lookout Harbour, Elephant Island, as a ' graded series of related 

 sediments ranging from limestones to impure types giving the amphibolites and garnet-hornblende- 

 schists rich in albite '. The amphibolites are closely associated, and even interbedded, with limestone 

 bands. Tilley surmises that the original sediments were somewhat abnormal inasmuch as abundant 

 albite was present. But there is one type of sediment, quite abundant and by no means abnormal, 

 which is often rich in soda and often rich in albite, namely, the impure sandstones known as greywacke. 

 The most typical greywackes are constituents of ancient fold-mountain ranges wherein they are 

 often associated with mudstones, slates, greenstones, ophiolites, and especially with igneous rocks 



