202 AUSTRALASIAN ANTARCTIC EXPEDITION. 



sedimentary rock by the igneous. The examples have been looked upon as igneous 

 phenomena, not metamorphic. Cole, for instance, describes a granite which, he claims, 

 has invaded and partially absorbed amphibolite. ' The various stages of absorption can 

 be traced with the unaided eye. Lumps of amphibolite seem to swim in the gneiss and 

 fade off into it, as if melting before our eyes. The gneiss becomes enriched with streaks 

 of basic matter in which biotite begins to predominate over amphibole."* The same 

 attitude has been maintained by Cole in his recent address to the British Association for 

 the Advancement of Science,t and a list of references is quoted where similar passages 

 between metamorphosed igneous and sedimentary rocks have been recorded in other 

 areas. As far as it can be verified, all the instances could be given a metamorphic 

 interpretation, in which case they become examples of metamorphic diffusion and pro- 

 vide evidence of the transfer of material during metamorphism. We cannot accept 

 Cole's statement that amphibolite is the " final term of various metamorphic series." 

 It is a statement in which considerable migration during metamorphism is tacitly 

 assumed, and it is an unwarranted assumption when we reflect that Cole is endeavour- 

 ing to apply the theory of contact metamorphism on the evidence of transition. 



A further example may be quoted from the Broken Hill region. Mawson states J 

 that where the metamorphic conditions are intense a passage of materials may take place 

 from the intrusive rock into the intruded rock. He instances a gradation between 

 quartzite and quartz felspar rocks east of Mookaie Hill. Mawson, however, is inclined 

 to regard these transitions as part of a pneumatolytic effect. 



An igneous magma may, of course, completely alter the character of the invaded 

 sediments, but there still remain to be found the examples where a junction has been 

 destroyed and replaced by transition types except where powerful stresses are evident. 

 Even with the play of stresses such junctions frequently survive, e.g., 12 miles north of 

 Casterton, Victoria, the junction of a foliated granite, presumably of Archaean age, 

 with the invaded sedimentary schists, is still perfectly sharp and transition types are 

 apparently absent. The fact that the bulk of the dyke rock has preserved its apparent 

 sharp junction with the grey gneiss is evidence that only special conditions will permit 

 metamorphic diffusion. Intrusions of igneous rock into igneous, with the junctions 

 subsequently modified by metamorphic diffusion, will necessarily be more difficult to 

 demonstrate than igneous intrusions into sedimentary rock. 



Summarising, we may assert that geological literature provides some evidence 

 for a molecular transfer during processes of recrystallisation. It has been found a difficult 

 matter to demonstrate, but the interpretation of the Cape Denison phenomena, with the 

 aid of solid diffusion, is probably applicable to a number of rock junctions partially 

 destroyed during metamorphism. If this is so a large number of unrecognised examples 

 involving migration is indicated. 



* " The Intrusive Gneiss of Tirerrill and Drumahair," G. A. J. Cole, Proc. E.I. Acad., vol. XXIV. B, pt. 4, p. 361. 



t G. A. J. Cole, Pres. Add Sect. C. Brit. Ass. Adv. Sci., Manchester, 1915, p. 5. 



% " Geological Investigations in the Broken Hill Area," D. Mawson, Mem. Roy. Soc. S.A., vol. II., pt. 4, p. 237. 



