126 PROCEEDINGS OF THE ALBANY MEETING 



Prof. R. T. Ohambeelin: I have listened to this paper with very great 

 interest. It seems to me that the fundamental importance of these experi- 

 mental researches and the resulting view that the rigidity of the rocks increases 

 with increasing depth below the surface can scarcely be overestimated, for 

 they are providing firm and solid foundations for the whole subject of earth 

 deformation. But there remains to be overcome one troublesome factor on 

 which some of us would welcome additional light. That is the evaluation of 

 the time element. I should like to ask Dr. Adams whether very much lesser 

 stresses acting through a much longer period of time, as would be the case in 

 the earth, might not produce the same results as the greater stresses acting 

 through a short period of time. Or has it been found possible in any way to 

 compensate for the short length of time included in the experiments and thus 

 minimize this troublesome factor? 



Professor Adams' reply to Professor Chamberlin : In order to eliminate the 

 time factor as far as possible, the experiments were arranged so that the rocks 

 were deformed with a very slow, uniform, creeping movement. The time factor 

 is discussed in the paper, but I am unable to state just how far it would influ- 

 ence the result. 



Eemarks were made also by Messrs. H. F. Eeid and Charles Schuchert, 

 with reply by the author. 



METAMORPHISM AND ITS PHASES 

 BY REGINALD A. DALY 



(Ahstract) 



An historical review of the word "metamorphism" discloses at least six 

 extant definitions. All are quite different in principle and yet all have been 

 actively used since 1900. A similar lack of unanimity is seen in the use of 

 "regional metamorphism," "dynamic metamorphism," "static metamorphism," 

 "contact metamorphism," "pressure metamorphism," "thermal metamorphism," 

 and most other names of the phases. The great need of a common vocabulary 

 relating to this subject has prompted the effort to frame definitions of the more 

 important terms. In the nature of the case, that program runs parallel with 

 the equally ditticult task of constructing a rigorous classification of metamor- 

 phic processes. 



A proposed classification follows : 



A, Regional metamorphism (not caused by eruptive bodies). 



I. Static metamorphism (erogenic movement not a causal condition). 



1. Stato-hydral metamorphism or hydro-metamorphism (low teni- 



perature). 



2. Sta to-thermal metamorphism or load metamorphism (high tem- 



perature). 

 II, Dynamic metamorphism (erogenic movement a causal condition). 



1. Dynamo-hydral metamorphism or slaty (?) metamorphism (low 



temperature) . 



2. Dynamo-thermal metamorphism or friction (?) metamorphism 



(high temperature). 



