THE METAMORPHIC ROCKS OF ADELIE LAND. 8TILLWELL. 35 



index and high double refraction. By comparison with other occurrences from this 

 area we record this mineral as allanite. The rock may be called a quartz biotite 

 amphibolite. 



No. 629. This specimen is a normal example of the hornblende rich varieties, 

 and it is especially interesting as it comes from the band which contains the xenoliths. 

 It contains the second highest percentage of hornblende, almost 70 per cent., in the series. 

 It is one of the massive types, and white felspar and dark hornblende are the only con- 

 stituents which are macroscopically distinguishable. As is usual with the massive 

 varieties the structure becomes granoblastic (Plate I., fig. 1), and the average absolute 

 grain size is approximately -22mm. The hornblende is green with the bluish-green tint 

 parallel to Z. As in No. 5, the hornblende is sometimes bordered and streaked with 

 paler coloured hornblende. Prism faces are well developed, but prismatic sections 

 always have a broken and ragged appearance. Sometimes the hornblende forms a 

 skeletal framework for felspar and quartz, and then a sieve structure (siebstructur) 

 appears. Like the hornblende, the felspar is in granular individuals. The majority 

 of it is clear and transparent, and there are two types present. Some clear calcic felspar 

 is found with an extinction of 35 measured from the trace of the broad lamellae and is 

 labradorite. The lamellae of the felspar are often confused and intermittent and dis- 

 crimination is difficult. A more sodic felspar is present which has a refractive index 

 less than 1-551, and sometimes greater than and sometimes less than 1-538. This felspar 

 is, therefore, becoming albitic. A quantity of the saussuritised felspar is present, and the 

 secondary clear felspar can be seen arising from the turbid mass. Green chlorite appears 

 in occasional skeletal plates showing the ultra-blue colour. It shows a transition to 

 biotite. Sphene, with its magnetite core, is a common accessory. Epidote and pyrite 

 are sparsely scattered through the rock. Lawsonite appears in microscopic veins in 

 some sections. This section is made from a specimen taken from the centre of the 

 outcrop. Sections made from specimens containing the xenoliths at the side of the 

 exposure show more lawsonite. These lawsonite veins are sometimes composite (Plate 

 I., fig. 5). There may be an epidote lining on the walls with lawsonite in the centre, 

 or there may be lawsonite on the walls with calcite in the middle. The abnormally high 

 percentage of hornblende and the low mica percentage are possibly to be associated with 

 the patches of epidosite and chlorite which were noted here. The rock is an amphibolite. 



No. 631. There is another example of the rocks with dominant hornblende. 

 Though the mica percentage is small the crystallisation schistosity is well marked. 

 The granoblastic structure is evident. The felspar is nearly all clear and transparent 

 and the proportion of saussurite is small. Occasional grains of quartz may be found. 

 The hornblende conforms to the crystallisation schistosity and some crystals enclose 

 felspar and blebs of quartz in a typically sieve-like manner. Brown biotite and sphene 

 are normal. Magnetite is scarce but in large grains bordered with sphene. Some 

 include prismatic sections of red-brown rutile. Minute crystals of apatite are enclosed 

 in all other minerals and lawsonite is rarely intergrown with biotite. The rock is an 

 amphibolite. 



