VOLUME XXVII NUMBER 6 



THE 



JOURNAL OF GEOLOGY 



SEPTEMBER-OCTOBER igig 



CRYSTALLIZATION-DIFFERENTIATION IN 

 IGNEOUS MAGMAS 



N. L. BOWEN 

 Queen's University 



INTRODUCTION 



A formal definition of the term magma is seldom given in 

 petrologic literature, but it is plain from most writings that the 

 word is intended to signify completely molten rock. Etymologi- 

 cally magma is perhaps more definitely applicable to a liquid with 

 much suspended solid matter, that is, to a sort of mush. In this 

 sense the term might designate igneous material in which crystalli- 

 zation was well advanced, and, while such usage should perhaps 

 not now be urged, it is none the less true that magma in this latter 

 sense is of fundamental significance in the genesis of igneous rock 

 types. In his paper discussing the crystalhzation of magmas^ 

 in which that process was advocated as the fundamental factor 

 in differentiation, the writer pointed out the special importance of 

 two stages, the early stage of crystallization, when crystal settling 

 may occur, and the late stage of crystallization, when squeezing out 

 of residual liquid may occur. Throughout most of the discussion 

 of crystallization-differentiation, however, particular attention was 



^ "The Later Stages of the Evolution of the Igneous Rocks," Jour. Geol., XXIII 

 (1915), Supplement. 



393 



