DEFINITIOX or METAMOrvPIIISM 6bL 



Teall (1888^ page 438) wrote of "metamorphism'^ : "This word is usu- 

 ally restricted in geological literature to clianges wliich a rock undergoes 

 in mineralogical or chemical composition and internal structure through 

 the operation of heat, heated water, or vapor, and mechanical agencies. 

 It is either local or regional/^ He excludes (page 410) weathering and 

 also the effects of ^'thermal waters, fumarole and solfataric action." He 

 recognizes only contact and dynamic (called "regional" in the earlier part 

 of his hook) metamorphism. 



Eeyer (1888, page 554) made metamorphism include the disintegra- 

 tion of rocks through weathering; the mere cementation of loose material 

 into coherent rocks; and the recrystallization of rock material in depth, 

 giving jiseudomorphism as an example. 



Harker (1889) published a brief general discussion of the nature of 

 metamorphism. Under that name he groups (page 15) "all processes 

 which result in a partial or complete crystallization or recrystallization 

 of solid masses of rocks.^' His "hydro-metamori^hism'^ implies low pres- 

 sure and low temperature and is illustrated in the deposition of inter- 

 stitial quartz during the conversion of sandstone into quartzite — a com- 

 mon kind of cementation. Harker prefers "thermo-metamorphism" to 

 "contact metamorphism," defining the former as alteration imder condi- 

 tions of low pressure and high temperature. Conditions of high pressure 

 and high temperature lead to "dynamo-metamorphism," while those of 

 high pressure and high temperature lead to '^plutono-metamorphism." 

 He states that dynamo-metamorphism implies "a direct correlation be- 

 tween mechanical and chemical energy." His classification is avowedly 

 made "for rough purposes." 



In his Traite de Geologic, de Lapparent (1893, page 584) defined meta- 

 morphism as including all changes "affecting rocks after their deposi- 

 tion"; and again (page 711) as "the sum of the chemical changes made 

 after the dej)osition of sediments." In another passage (page 612) he 

 expressly states that the alteration of rocks by the weather and by the 

 penetration of surface waters is to be regarded as a metamorphic process. 

 Yet throughout tbe long sections of his book that deal with weathering 

 and the effects of percolating water the words "metamorphism" and "meta- 

 morphic" never appear. Instead, he uses ^'alteration" and "transforma- 

 tion." In practice, therefore, he found it unnecessary to use "metamor- 

 phism" according to either of his l)road definitions. 



Zirkel (1893, I, page 57,2) designated metamorphism as the phenom- 

 enon "that a given rock has, through a geological canse which is independ- 

 ent of the original formation (Bildiing) of that rock, undergone such a 

 change that a well characterized new rock iype is developed." He ex- 

 cludes weathering from its list of phases. 



