CHAPTER III. 

 THE METAMORPHOSED DYKE SERIES OF CAPE DENISON. 



1 . NOMENCLATURE. 



The nomenclature generally adopted in the following pages is that taught in the 

 " Die Kristallinen Schiefer."* Grubenmann's treatise deals with schists and gneisses 

 which have developed by the thermo-dynamical alteration of pre-existing rocks. He 

 has told us what rocks belong to the crystalline schists, and in these the effects produced 

 by the alterations completely determine the character of the rock. 



Various meanings have been attached to the term " metamorphic rock," and we 

 are in general agreement with the criticism of this term given by Crookf. Crook points 

 out that Van Hise's use of the term is too broad, as it is made to include all rocks, 

 and that there is no satisfactory definition of the term ; either it is made too incomplete 

 or too comprehensive in its meaning, and he desires to exclude a group of metamorphic 

 rocks from the fundamental rock classification into igneous, sedimentary, and 

 metamorphic. The old group of metamorphic rocks is replaced by several groups, 

 including a group of thermo-dynamically altered rocks which are unfused and unmodified 

 by exudations. This group seems to correspond with the Kristallinen Schiefer. If 

 we adopt this subdivision, are we to exclude the term " metamorphic " from our nomen- 

 clature ? We are inclined to think that the term is too deep rooted and too convenient 

 to permit this. It is therefore necessary to state that in the following account of the 

 metamorphic rocks of Adelie Land we use the term in the limited sense indicated in 

 Grubenmann's work and adopted by Johnston and NiggliJ. We are dealing with 

 rocks which come under the heading of the crystalline schists, and when we refer to a 

 rock as metamorphic we imply that it falls into the group of the crystalline schists. 



Its use in this way comes partly from the want of a general rock term for those 

 members of the crystalline schists which possess a massive texture in contrast to the 

 schistose or gneissic texture. The terms schist and gneiss are not fundamentally 

 different, and the same processes produce the foliation of the gneissic granites and the 

 foliation of the sedimentary gneisses. A gneiss can be looked upon as a schist with an 

 imperfect schistose structure ; and should this structure become too insignificant to 

 be noticeable, what shall we call the rock ? Sederholm has considered that it is 

 impossible to give the term " gneiss " a limited meaning, and he believes that it must 

 remain a comprehensive name with a very wide significance. We find that this wide 



Die KmUUinen Schiefer." U. Orubenmann, Berlin, vol. I., 1904, voL IL, 1907. 



f " The Genetic Classification of Rocks and Ore Deposits," T. Crook, Hin. Mag., vol. XVII., p. 69. 



J " Principles Underlying Metamorphic Processes," Johnston ft Niggli, Journ. Oeol., vol. XXI., p. 481. 



| " Om granit och gnei," J. J. Sederholm, Eng. Summary, BulL Com. Geol. Fin., No. 23, 1907, p. 109. 



