ADDITION^AL DESCRIPTIVE TERMS 418 



Properly guarded, thermal metam.orpMsm might signify changes ef- 

 fected by high temperature. The use of this expression would, however, 

 imply that the field observations do not sufhce to make clear what is the 

 source of heat — mere burial, dynamic action, or igneous intrusion. If 

 water and high temperature! had essentially cooperated, and again, if 

 outcrops failed to show the source of heat, hydrothermal metamorphiwi 

 might similarly be employed. 



Katamorpliisni and anamorphism, denoting contrasted phases of rock 

 alteration in general, seem likely to persist as useful descriptive terms. 

 They represent a problem in the classification of processes which is quite 

 different from the problem attacked in this papei-, and the favored defini- 

 tions of "metamorphism" and its subdivisions do not conflict with those 

 of the two key words employed l)y Yan Hise or Leith and Mead. 



H. C. Sargent (1917, page 59) has proposed ^'auto-metamorphism" as 

 a name for the intense decomposition of spilite, "due to retention of vola- 

 tile constituents resulting from the physical environment of a submarine 

 flow." 



Finally, if a formation has been recrystallized more than once, it may 

 be said to have undergone superimposed metamorpliisms, or, more com- 

 pactly, as suggested by Teall (1888, page 8), superposed mefamorpMsms. 

 An adjective proposed by Koenigsberger (1910, page 670) suggests poly- 

 mefamorphism as a synonym. 



Ultra-metamorphism 



Sederholm (1907, page 102) has called the complete remelting of a 

 rock anatexis. With him one may describe anatexis as a phase o»f '"uUra- 

 metamo7'pliism" (Holmquist, 1909) without running counter to the pro- 

 posed definition of metamorphism. The course of the melting-up may 

 be purely thermal or it may be hydrothermal. Sederholm (1907, page 

 102) makes the emanation of gases and lieat from the general subcrustal 

 region of the earth responsiljle for tlie palingenesis (rebirtli) of Pre- 

 cambrian granitic magma in siiu. 



Several French geologists, including Termier and Ilaug, still believe 

 tliat the rise of hot gases from the earth's interior has generated the post- 

 Cambrian batholiths from geosynclinal sediments. This extremely doubt- 

 ful thesis regarding the geological efficiency of "colonnes filtrantes" is a 

 matter relatijig to ultra-jnetamorpliism latlier than to metamorphism. 



"Eoches d'im])il)ition" result from contact jneiamorphism. They may 

 graduate into complexes developed by 1 it-par-lit injection, which is com- 

 monly simultaneous with regional motainorphism and also a cause of con- 

 tact metamorphism. But several considerations forbid belief that any 



