188 AUSTKALASIAN ANTARCTIC EXPEDITION. 



The general similarity in field characters and in composition at the four localities 

 permit the assumption that the altered dykes in each area are part of one intrusive 

 series. Differences in all cases can be ascribed to varying metamorphic conditions. 



There is no direct evidence to correlate this intrusive dyke series with the Cape 

 Denison metamorphosed dyke series ; but all differences can again be explained by 

 varying metamorphic conditions. The dominating factor among the metamorphic 

 conditions at Cape Denison is strong stress, whereas the general metamorphic conditions 

 in the Cape Gray series involve high uniform pressure and high temperature with only 

 subordinate stress. The strong stress at Cape Denison has destroyed all those finer 

 features of dyke form which have been preserved at Cape Gray. The differing mineral 

 suites are considered to be a direct reflection of the different conditions during 

 recry stallisation . 



CORRELATION. 



The basic pyroxenic gneisses are found in many areas of the crystalline schists. 

 In the classical area of the Saxon pyroxene granulites there are examples to which 

 members of the Cape Gray series are analogous. The fine grained plagioclase pyroxene 

 gneiss (No. 773) is similar to the pyroxene granulite from America near Penig.* This 

 Saxon type, however, is described as schistose, whereas the Cape Gray rock is massive 

 and relic dolerite structures are recognisable. There is an analogy between the garnet 

 amphibolite from Stillwell Island (No. 953) and the pyroxene granulite from Bahnstation, 

 Wittgensdorf ; f but the hornblende in the former is replaced by pyroxene in the latter. 

 The manner in which the garnets are set in a colourless base in the Antarctic rocks is 

 a phenomenon that also appears in the Saxon rocks illustrated on Table XXIII., figs. 

 3, 5, and 6, of Lehmann's memoir. There is also a likeness between the pyroxene 

 granulite from Chemnitzbiege, by Mohsdorf,J and the amphibolite No. 769 from Garnet 

 Point. In No. 769 there is little garnet, but the structures are similar in both. In 

 this Saxon example Lehmann considers that the separation of the pyroxene occurs 

 at the expense of the garnet, whereas Holland has found the reverse to be true in some 

 of the Indian rocks. Other observers have formed similar conclusions to both Lehmann 

 and Holland. In our observations we have been led to suspect evidence for Lehmann's 

 position and we obtained definite proof in favor of Holland's position. The explanation 

 probably lies in the fact that the reaction which involves both pyroxene and garnet 

 is a reversible one. The direction in which the reaction goes is determined by the external 

 conditions. 



The same class of rock has been described among the pyroxenic and hornblendic 

 gneisses by Lacroix, in India and other places. || The pegmatoidal pyroxene, set in 

 oligoclase and quartz, that is figured by Lacroix (p. 179) is similar to some of the structures 

 described as diablastic, e.g., No. 942. 



* " Entstehung der Altkrystallinischen Schiefergesteine," J. Lehmann, Bonn, 1884, Tafel XXIII., fig. 2. 



t Tafel XXIII., fig. 3. 



t Tafel XXIV., fig. 5. 



" Origin and Growth of Garnets," T. H. Holland, Rec. G.S.I., vol. XXIX., p. 20. 



|| " Gneissose Rocks of Salem and Ceylon," Lacroix, trans, by Mallet, Rec. G.S.I., XXIV., p. 155. 



