296 AUSTRALASIAN ANTARCTIC EXPEDITION. 



It was noted that epidote was sometimes developed as a result of the alteration 

 of the garnet. Van Hise * gives the following equation for the development of epidote 

 from a lime-iron-alumina garnet 



2 Ca 3 Al 2 Si 3 12 . Ca 3 Fe 2 Si 3 12 + 5 C0 2 + H 2 O = 2 HCa a Al 2 FeSi 3 13 + 5 CaC0 3 



+ 3 Si0 2 + k (heat liberated). 



In the rocks under discussion, however, calcite is only present in No. 348 where it appears 

 to be derived from calcic plagioclase. In the epidote-magnetite-schist No. 989 and 

 the magnetite-garnet-schist No. 245 epidote is developed from the garnet but there is 

 no free calcite. The above equation therefore represents a garnet with more lime than 

 in the garnets of these rocks. 



Van Hise* records that in all cases of alteration of garnet, quartz appears among 

 the secondary minerals. In these rocks magnetite is also as general. 



III. POSITION IN GRUBENMANN'S CLASSIFICATION OF CRYSTALLINE 



SCHISTS. 



The described rocks can be considered in two groups (1) those in which 

 magnetite is the most important constituent ; and (2) those in which garnet and magnetite 

 are equally important. 



The members of the first group can be placed in the group of iron oxide rocks 

 (magnetite rocks) which forms Grubenmann's Xlth group. The presence of garnet, 

 quartz, plagioclase, orthoclase, biotite, magnetite, &c., and the occurrence of homo- 

 blastic and diablastic structures, which are sometimes almost obliterated by later epi 

 structures, all necessitate some form of deep-seated metamorphism. In addition, a 

 transference to epi zone conditions is suggested in some cases by the hydrous minerals 

 associated with the kaolinisation and sericitisation of the felspars and with the 

 development of chlorite and magnetite from garnet and biotite. Thus the magnetite 

 schists and gneisses Nos. 576, 912, 933, 294, and 55 are considered to be epi-meso rock 

 types, but may fall into the family of epi-magnetite rocks of Order III. In Nos. 989, 

 527A, and 889 the first metamorphism may have resulted from either meso or kata 

 conditions. No. 889, a magnetite-garnet-schist containing cordierite, may be related 

 to the aluminous silicate gneisses (Group II) and the family of kata garnet gneisses. 

 Nos. 765, 926, and 296 appear to be pure meso zone types and belong to Order II, meso 

 magnetite rocks and micaceous hematite schists (Group XI). 



* " Treatise on Metamorphism." C. R. Van Hise. Geol. Surv., U.S.A., monograph 47, 1904, p. 305. 



