OLASSTFICATIOX OF METAMORnilC TEOCESSES 411 



lessening the intensiveness of each. The prevailing conflicts of defini- 

 tions threaten to destroy tliese terms as practical aids in geology. To 

 save them/ no l)etter conrse offers itself than to seek the factor common 

 to the largest nnmher of definitions for each of the vrords. With that 

 common factor in supreme control of the definition^ the word loses depth 

 of meaning, hut, as a rnle, gains l)readtli and, above all, capacity for 

 logical, clean-cnt description and usage. 



The four compound names — "stato-liydral," ^^stato-thermal," "dynamo- 

 hydral," and '^dynamo-thermal metamorphism'' — are directly founded on 

 root words already familiar and are mnemonically easy to locate in the 

 scheme. They are, however, somewhat cmnhrous and har])arous in form ; 

 synonyms of simpler make would, therefore, l)e welcome. The suggested 

 equivalents, resjoectively, "iiydro-,'' "load," "slat}^,'' and "friction meta- 

 morphism'' are arbitrarily defined fi'om the standpoint of the literal 

 meaning of each adjective. "Slaty'' and "friction" have been adapted 

 for the present purpose with some misgiving. The writer has not yet 

 been able to find adjectives that might immediately suggest the ideas in- 

 volved; more than usually in the proposed system, the technical names 

 are here figurative rather than fully coiniotative. In practice the geol- 

 ogist seldom Jiecds to distinguish under separate names "dyiiamo-hydraP' 

 and "dynamo-thermar' metamorphism. 



The adjectives most likely to l)e useful in the future are "regional," 

 "local,'' "static," "load," "dynamic," "contact," and "load-contact." The 

 sanction of each of them is founded on theory of origins. General agree- 

 ment in definition is bonnd to be indirectly proportional to the respective 

 amounts of theory implied in these seven words. For the student of post- 

 Cambrian rocks, the terms "regional metamorphism," "local metamor- 

 phism," "dynamic metamorphism," and "contact metamorphism" may 

 be in constant use; "static metamorphism" is likely to be less in demand; 

 "load metamorphism" and "load-co]itact metamorjDhism" are still less 

 in active demand. For iho student of the Precambrian complexes, all 

 seven phases need expression, ])ut he should feel the special need of "load 

 metamorphism" and "load-contact metamorphism." Until the peculiar 

 conditions of Precaml)rian time have been sensed and compared with 

 later conditions, it is impossible to make a permanent definition of meta- 

 morphism or a universally acceptable classification of its phases. 



The problem of metamorphism thus remains, where it has always been^ 

 chiefly in the hands of workers specializing in the Precambrian terranes. 

 Intensive research on younger formations and lal)oratory experiment are 

 both extremely valuable, but the field i]ivestigator of the Precambrian 

 rocks must make his unique and first-rank contribution to the necessary 

 sum of facts. To him especially the writer offers definitions and classifi- 



