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AUSTRALASIAN ANTARCTIC EXPEDITION. 



The terms " gneiss " and " schist " are used in the sense denned by Holmes.* 

 Grubenmann's usagef of the terms " texture " and " structure " is adhered to. In 

 this, the structure is understood to be determined by the form and relative size of the 

 components of the rock. He adds that the structures appear to be functions of the 

 chemical composition of a rock, and of the magnitude of the temperature and pressure 

 and the time interval during metamorphism ; and are also dependent on the strength, 

 ability, and speed of crystallisation of the minerals developed. The texture is the 

 spacial arrangement of the constituents, and he states that the textures are not so 

 much dependent on the nature of the rocks as upon external circumstances. 



II. PETROGEAPHY. 



1. MINERAL COMPOSITION. 



Rosiwal determinations of some of the specimens have been made in order to 

 express quantitatively their mineralogical content. These measurements were made 

 on sections cut at right angles to the schistosity and the results are expressed in Table I. 

 Generally it was found expedient to determine the quartz and felspar together. In 

 Table I below, iron ore includes magnetite, ilmenite, pyrite, &c., while " p " signifies the 

 presence of a mineral in small quantities. A Rosiwal determination of a magnetite- 

 garnet rock from Broken Hill, New South Wales, is added for comparative purposes. 



In some rocks, mostly of fine-grained nature, the magnetite percentage alone 

 was determined. These form Table II, and Table III gives the specific gravities of the 

 remaining specimens. The figures for the various minerals as stated in percentages 

 present. 



TABLE I. 



* " The Nomenclature of Petrology." A. S. Holmes, London, 1920, p. 107. 



t " Structur und Textur der Metamorphischen Gesteine." U. Grubenmann. Fort, der Min., Krjst. und Pet., Band II- 

 1912, p. 209. 



| Approximate. 



