394 R. A. DALY — :metamorpiiism a^d its rilASES 



ground that all metamorpliism nieaiis movement — of mass or molecule. 

 The same principle would destroy "pressure metamorphism/' for all 

 metcimorphism takes place under some pressure, and "load metamor- 

 phism/"' for all metamorphism takes place under some load. In a literal 

 sense nearly all metnmor})hism is "hydro-metamorphism," since water is 

 a participant in most recrystallizations in rocks. Similarly, all meta- 

 morphism is "thermal metamorphism," for some heat is indispensable 

 tliroughout. Ha-P2^i]y, the inventors of the names here considered have 

 ]iot been bound by verbal form. They have treated words as tools and 

 not as masters; as representative and not as directly connoting all the 

 ideas symbolized by the ijidividual words. 



A brief survey of the varieties of usage will aid in choosing, for some 

 of the terms employed in the proposed classification, those definitions 

 that seem best to meet the present and future needs of geological science. 

 After that review, a few other ex2)ressions appearing in the scheme will 

 be introduced and discussed. 



DEFINITION OF REGIONAL METAMORPHISM AND LOCAL METAMORPHISM 



Three different meanings have been assigned to "regional metamor- 

 phism.'' Its originator, Daubree (1860, page 59), did not define it for- 

 mally. As already noted, he saw in it an improvement, as a synonym, on 

 tlie "normal metamorphism'' of de Beaumont, Yirlet, Naumann, and 

 others. Daubree thus seems to have intended the expression to cover only 

 those changes in rocks which are due to simple burial and the emanation 

 of heat or hot gases from the earth's interior. In this sense Brauns 

 (1896, page 278), Termier (1903, page 581), Doelter (1906, page 175), 

 Coleman (1910, page 615), and Tornquist (1913, page 18) use the term. 



Prestwich (1886, page 408), Teall (1888, page 418), de Lapparent 

 (1893, page 1574), Eosenbusch (1910, page 72), Scott (1911, page 409), 

 Flett (1911), page 219), and Holmquist (1916, page 145) define or use 

 it as equivalent to "dynamic metamorphism." 



A. Geikie (1903, page 766), Kemp (1908, page 113), Pirsson (1915, 

 page 319), Eies and Watson (1915, page 208), and F. W. Clarke (1916, 

 page 583) describe regional metamorphism as that kind which, by its 

 nature, is likely to affect extensive areas, and do not inject into its defini- 

 tion any reference to the cause of the alteration beyond the statement 

 that the rock alteration is not genetically connected tuith the eruption of 

 magma. 



The third definition has many adherents other than those Just named. 

 They have felt the necessity of a term with just this limited connotation, 

 simple and somewJiat negative as it is. Abundant experience has set up 



