no 



AUSTRALASIAN ANTARCTIC EXPEDITION. 



crystallisation of the central portion. When the pressure is relieved the crystallisation 

 proceeds normally and the centre becomes massive. Non-uniform pressure is essential 

 to produce the gneissic banding, and it cannot be applied to a liquid. Therefore, not 

 until the magma has become frozen and solid can the gneissic character be impressed 

 upon it. We find no satisfaction in Van Hise's statement* that " the parallel orientation 

 of minerals in the original gneisses formed from magmas is due to differential stress 

 during the primary crystallisation of the rocks." 



-U+.l+.J.+'-U ~~-^ +"-,_ "*" ~*"_U-|--L_~ t ~-l_" ( ~ 



+ -J- 4- ~t- -t- -t- -h -p -f- -f- -H 

 4--H4- 4-4--I-4-4-4--4- 



4- 4- + -h .JxdUJ- 4- 4- 4- > 

 4- 4- 4- 



4- 



Fig. 10. 



DIAGRAM SHOWING THE FORMATION OF A SCHISTOSE MARGIN WITHOUT 



ANY APPEAL TO MOVEMENT IN THE MAGMA. HYDROSTATIC PRESSURE 



IN THE MAGMA is EXERTED AGAINST THE MARGINAL RIM AS NORMAL 



STRESSES, WHICH INDUCE RECRYSTALLISATION AND SCHISTOSITY. 



In Wright's experiments he aimed at producing crystallisation, and with it 

 schistosity, from solution under strain. He does it by heating a solid, viz., glass, under 

 strain. He looks upon glass as an undercooled liquid, but it can equally well be named 

 a solid solution, as glasses fall within Van HofE's definition of a solid solution. He 

 really shows that crystallisation within a solid, not crystallisation in a liquid under 

 strain, produces the schistosity. The difference between the liquid and the solid 

 becomes, of course, a fine point when viscous substances are being considered, though 

 the difficulty could be arbitrarily settled by looking upon a viscous mass as solid as 

 soon as it can take a stress. It cannot be inferred from his experiment that schistosity 

 can be produced in the first crystallisation of a cooling magma. 



From these considerations it is necessary to strongly oppose the use of the terms 

 " flowing gneiss " and " fluxion gneiss " which constantly appear in geological literature 

 dealing with metamorphic rocks. To be consistent it is also necessary to oppose the 

 introduction of the term " injection foliation," proposed by Flett, because it likewise 

 carries false meaning. A term " injecting banding " may be appropriate for the banding 

 which Geikiet considers is produced by the injection of aplitic magma into dark schists 



* " Treatise on Metamorphism," C. R. Van Hise, p. 782. 

 t " Text Book of Geology," A. Geikie, p. 256. 



