108 AUSTRALASIAN ANTARCTIC EXPEDITION. 



Though Becke has explained in 1892 that dynamo-metamorphism may involve 

 either complete recrystallisation, resembling contact metamorphism, or granulation, 

 there arose a tendency in the following years to associate only mechanical structures 

 with pressure effects. This tendency produced Weinschenck's attack on the use of the 

 term " dynamo-metamorphism " which is declared to be vague, and to connote the 

 personal interpretation of the user. Weinschenck's attack is directed mainly against 

 the idea of purely mechanical transformation of rocks. Grubenmann* has approved 

 of this criticism, but he opposes the introduction by Weinschenck of the terms " piezo- 

 crystallisation " and "piezo-contact-metamorphism." " Piezo-crystallisation " is the 

 crystallisation which proceeds in a magma under the influence of a tangential thrust 

 and produces primary pressure banding. ' Piezo-contact-metamorphism " is the 

 influence exerted by the intrusive magma and its attendant gases or vapours on 

 the enveloping rocks during " piezo-crystallisation." The ideas are introduced by 

 Weinschenck to explain the large area of metamorphic schists surrounding the central 

 massif of the European Alps. Grubenmann maintains that these terms are unnecessary, 

 as the kind of metamorphism is explained as soon as the fundamental physico-chemical 

 factors are denned. The special terms are superfluous provided we consider collectively 

 the temperature, the uniform pressure, the stress (non-uniform pressure), and the factor 

 of the individual substance at the time of the metamorphism. In this Grubenmann 

 is dealing with rocks which undergo no essential change in composition during 

 metamorphism. Metasomatic changes and all rocks whose composition is changed by 

 igneous exhalations and heated waters are not considered. Johnston and Nigglif 

 have reached the same conclusion in their exposition of the general principles underlying 

 metamorphic processes. 



Grubenmann, Van Hise, and others have attempted to classify these conditions 

 of temperature, etc., by reference to zones of metamorphism when each zone is 

 characterised by special conditions which grade into the special conditions of the 

 neighbouring zone. Crook has adversely criticised the value of the conception of 

 metamorphic zones as given by Van Hise, partly because the crustal zones fail to provide 

 a basis of genetic classification of rocks either in a general or metamorphic sense, and 

 partly because he believes in the " paramount importance of igneous intrusions as agents 

 of metamorphism "J. Provided, however, that the zones are made sufficiently 

 definite, and are not made dependent on depth within the earth's crust, they are very 

 useful in defining the sets of conditions under which changes occur. 



Rock flowage is a term that frequently appears in portions of the literature on 

 metamorphic geology, but no use is made of it in our discussion. It is, no doubt, a 

 useful term in structural geology, when, for structural considerations, the earth's crust 

 is divided into a zone of fracture and a zone of rock flowage. Deformation of the rocks 

 occurs in the former by fracturing, and in the latter by rock flowage involving a 



* " Die Kristallinen Schiefer," vol. I., p. 46. 



t " The General Principles underlying Metamorphic Processes," Johnston and Niggli, Journ. Geol., voL XXI., p. 63. 



t " The Genetic Classification of Rocks and Ore Deposits," T. Crook. Min. Mag., vol. XVII., July, 1914, p. 55. 



