238 AUSTRALASIAN ANTARCTIC EXPEDITION. 



so that the presence of sesquioxides is indicated. As a whole the pyroxenes may be 

 regarded as hedenbergitic rather than diopsidic. A parting parallel to the 001 face 

 is often developed (cf. No. 1168). 



Epidote is a very characteristic mineral of these rocks, present in irregular grains' 

 and again as narrow rims to other minerals. A basal cleavage is usually strongly 

 manifest. The extinction in sections parallel to the optic axial plane is approximately 

 30 from the 001 cleavage. The optic sign is negative, with the optic plane perpendicular 

 to the cleavage. It is strongly pleochroic in yellowish -green tints, and a high content 

 of Fe 2 3 is indicated by a high birefringence of 0-04 (as in No. 38). Intergrowths 

 with quartz are not uncommon. 



A potash felspar with microdine twinning is present in variable amount, and 

 calls for no special remark. 



Scapolite is present in Nos. 38 and 310, but is absent in the remaining rocks. 

 It has the high birefringence of the scapolites of the pyroxene garnet rocks. In No. 38 

 it may be surrounded by a narrow shell of basic plagioclase. In many cases this cannot 

 be regarded as a secondary development of scapolite from plagioclase, as the boundaries 

 are quite sharp. Rather it has the appearance of primary growth, and suggests that 

 plagioclase appeared in place of scapolite when the supply of essential mineralisers for 

 the formation of the latter mineral became exhausted. 



Bluish-green actinolite is present in No. 996, but is absent in the other rocks. 

 It forms independent crystals in the rock. 



Quartz is sparingly distributed in these rocks, and very characteristically in 

 association with epidote. Its presence here suggests that it is a by-product in the 

 synthesis of epidote. 



Two single grains of pleochroic' tourmaline are observed in No. 996. The 

 pleochroism scheme is 0>E with =- dark green and E - reddish -brown. 



(6) EPIDOTE-MARBLES. 



The rocks of this class are Nos. 132, 305, 308, 384, 386, 534, 654, 676, 995, 997, 

 and 1163. As a class they are fine-grained rocks, which on weathered surfaces show 

 an abundant development of yellow-green epidote. Some of them are banded, due 

 to streaks and lenses of this mineral, and irregular segregations can often be observed. 



The constituent minerals are calcite, epidote, actinolite, microcline, plat/itx-liisc. 

 titanite, biotite, quartz, chlorite, apatite and magnetite. 



Calcite shows abundant lamellar twinning, and the grain -size is very variable. 

 It is especially fine-grained in rocks Nos. 305, 386, 534, and 1163. In some examples 

 distorted twin lamellae and mortarisation of the larger calcite grains (as in No. 997) 

 bear witness to the shearing movements which have affected the rocks. 



