THE METAMORPHIC ROCKS OF ADEL1E LAND. STILLWELL. 49 



example in the collection of such a crystal is lin. broad, and shows the re-entrant angle 

 of a simple twin (Plate X., fig. 6). In other cases the saussurite masses are both rounded 

 and angular. The largest rounded mass among the specimens in the collection is 2in. 

 in diameter. A remarkable example of an angular mass of saussurite is shown on Plate 

 X., fig. 5. Here the section is a perfect triangle, with the sides measuring 2in., If in., 

 and If in. The boundary is macroscopically sharp, except for a minor length which 

 is a little ragged at the left hand corner and which is scarcely noticeable in the 

 photograph. A small amount of hornblende and epidote is macroscopically visible 

 in this example. In all cases the junction between the saussurite and the amphibolite 

 is normally sharp, irrespective of the crystalline, angular, or rounded nature of the 

 contour. Some examples, which are illustrated on Plate IX., fig. 4, consist of 

 amphibolite uniformly and thickly studded with small patches of saussurite averaging 

 Jin. in diameter. A boulder found on the lower moraine a little north of the outcrop 

 is used as the diagram, but similar examples collected in situ are in the collection. The 

 appearance is that of a porphyroblastic amphibolite, though there is considerable 

 variation in size. Such would be a likely explanation were they not only found in 

 association with the better defined meta-xenoliths. 



Macroscopically the saussurite is a compact, stony mass, in which one can sometimes 

 distinguish black specks of hornblende, green crystals of epidote, and, more rarely, 

 white patches of calcite. Thin sections of this type reveal the crystalline aggregate 

 known as saussurite. The larger xenoliths have produced relatively coarse crystalline 

 aggregates wherein identification of the constituents has become possible (Plate II., 

 fig. 4). 



A good portion of the aggregate is always a cloudy, brightly polarising mass similar 

 to the saussuritised felspar, to which reference has been made in dealing with the previous 

 rock types. At times a system of parallel lines, defined by thin lines of hematite or 

 limonite, are observed in parallel light, and these represent traces of the broad lamellae 

 of the primary felspar. In rare instances relics of the primary felspar itself are found. 

 In such cases the bulk of the crystal has been saussuritised, and only a few clear lamellae 

 are left. A section was found normal to these primary lamellae and gave an extinction 

 angle of 44, measured from the lamellae bands. The primary felspar is highly calcic 

 and near the anorthite end of the series. 



In the confused aggregate epidote is prominent, and the large grains can be 

 recognised at once by the brilliant polarisation colours. It is a very pale epidote with 

 feeble pleochroism in the thin section and with the (001) and the (100) cleavages well 

 developed. The optic axial plane is normal to the cleavages as usual, and from the 

 (001) cleavage the extinction angle is approximately 25, and from the (100) it is approxi- 

 mately straight. The outline of the large pieces is usually granular, but sections showing 

 two cleavages with crystal boundaries may be found. Sometimes the larger grains 

 are bordered with finely granular masses of a rather darker epidote. The latter is 

 much more abundant in some sections than in others, and it seems to mark a stage in 



i A, VoL m.. Part 1 D 



