;)8-l: K. A. DALY METAMOKrillSM AND ITS PHASES 



iuclude (page 485) certain clianges induced by moderate deformation. 

 Besides contact metamorphism, Eosenbnsch admitted only dynamic meta- 

 morphism, which he named in 1886. For the latter Eosenbnsch gave 

 regional metamorphism, mechanical metamorphism, and dislocation meta- 

 morphism as synonyms. On page 73 is the following definition (in 

 translation) : ^^As dynamo-metamorphism we designate the siim of the 

 changes in the mineralogical constitution and structure of a rock, due to 

 the effect of orogenic processes. . . . We regard pressure as the op- 

 erating factor in dynamo-metamorphism, without specifying Avhether 

 pressure acts directly, as such, or indirecth', as, for example, through a 

 rise of temperature." A further indication as to what he thought con- 

 cerning the real nature of metamorphism as a whole, a passage on page 

 575 may be quoted, in translation: "The crystalline schists are eruptive 

 or sedimentary rocks which have undergone geological transformation 

 under the essential control of the geo-dynamic phenomenon [^Gebirgs- 

 druck,' orogenic pressure] .'' Throughout his writings there appears to be 

 no hint that load metamorphism need be considered. 



Apparently Grubenmann excludes weathering and ordinary cementation 

 from the field of metamorphism. However, he adds to the complexity of 

 the problem by dividing (1910, page 45) rock transformations into three 

 classes: a, metamorphism in the narrower sense; 1), contact metamor- 

 phism; and c, metamorphism by magmatic injection and assimilation. 

 Though he explains the crystalline schists as chiefly the product of moun- 

 tain-building, he recommends (page 126) that the term "dynamo-meta- 

 morphism" be wholly given up, since it easily leads to the wrong notion 

 that purely mechanical or pressure phenomena are implied. He actually 

 suggests that the simple word "metamorj^hism" should be used in its 

 place ! 



Scott (1911, pages 406 and 409) defines metamorphism as the '^pro- 

 found transformation of a rock from its original condition by means other 

 than those of disintegration." He believes that the consolidation ol sedi- 

 ments should be regarded as a phase of metamorphism, yet groups its 

 processes in two classes only, under the captions contact metamorphism 

 and regional or dynamic metamorphism. 



Lindgren (1913, page QQ> to 69) writes that metamorphism "has lately 

 been employed in a wide sense, so as to cover any change in the com- 

 position and structure of a rock, through whatever agency and Avith or 

 without gain or loss of substance. In this wide sense the term would 

 include weathering and ordinary alteration of rocks at no great depth. 

 This usage was adopted by Yau Hise, but is not generally accepted, and 

 tlie tendency seems to be to reserve tlic term for cases where the trans- 



