THE METAMORPHIC ROCKS OF ADELIE LAND. STILLWELL. 31 



and sometimes the biotite in the hornblende. The felspar appears in rounded and 

 indented grains. A few scattered grains only are clouded. It is generally perfectly 

 clear and transparent, and there seem to be two types of plagioclase, and possibly also 

 orthoclase. The bulk of the felspar is untwinned. A few grains with lamellar twinning 

 give values between 20 and 27 for the extinction angle. This is best interpreted 

 as andesine. From ground-up powder of the rock refractive index was found to be less 

 than 1-542 in some cases, but mostly between 1-542 and 1-551. In the section the 

 refractive index was rarely found below that of Canada balsam. Hence the bulk is 

 probably andesine with a few grains of either orthoclase or albite. Quartz is present 

 as a very minor constituent and has an appearance very similar to the clear felspar. 

 It can only be distinguished with certainty from the felspar by the use of convergent 

 light, and considerable search is required to find a uniaxial figure. The hornblende is 

 definite and strongly pleochroic. Its colour scheme is X, greenish yellow ; Y, bright 

 green ; Z, bluish green. It has an extinction up to 15 in prismatic sections. Sphene, 

 exceeding 3 per cent., is conspicuous in wedge-shaped crystals and in grains. It conforms 

 to the schistosity, and frequently encloses an idioblastic crystal of magnetite. It is 

 also occasionally associated with rutile. Epidote (8-9 per cent.) is more abundant 

 in this rock than in any other member of the series except when found in segregations. 

 It appears in pleochroic lemon-yellow crystals, commonly idioblastic, and shows the 

 brilliant polarisation colours of the third order. It does not possess the same dark 

 border of colour as sphene, and the polarisation colour of sphene usually reaches the 

 high order whites. In rare cases it is found intergrown with zoisite (or clinozoisite). 

 Colourless apatite is a notable accessory, and its crystals are at times comparable in 

 size to the sphene grains. Magnetite is present in the same proportion as sphene and 

 is sometimes idioblastic, apart from the sphene enclosures. Cubes of pyrite are very 

 sporadic. Fluorite is not infrequently found in irregular isotropic blue grains, but 

 it may be intergrown with the biotite after the manner of chlorite. No. 153 may be 

 called an epidote biotite schist. 



No. 5. This specimen has been referred to as abnormal. It possesses a slightly 

 coarser grain size than the average. The crystallisation schistosity is less marked 

 and there is a tendency to a massive texture. The structure at the same time becomes 

 more granoblastic. Apatite, epidote, and sphene especially participate in the increased 

 grain size and now appear in grains comparable in size with the felspar and hornblende 

 crystals. The percentage of epidote is noticeably high in comparison with the mica 

 content, and we can recall a field note stating that the precise locality of No. 6 

 is especially rich in epidote. Epidote and, to a less degree, fluorite are especially 

 abundant in seams and joint planes at this point. A further characteristic of the 

 sample is the replacement of biotite by the green pleochroic chlorite which frequently 

 gives the ultra blue polarisations colour. The chlorite plates are usually associated 

 with and penetrated poikiloblastically by well-formed epidote, clear felspar (which 

 looks like quartz), and stray grains of magnetite. The green hornblende is abundant 

 and idioblastic in sections, showing two cleavages. The terminal faces of prismatic 

 sections are not developed. At times the hornblende is streaked and fringed by much 



