VOLUME XXX SUPPLEMENT TO NUMBER 6 



THE 



JOURNAL OF GEOLOGY 



August-September ig22 



SUPPLEMENT 



THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 



N. L. BOWEN 

 Geophysical Laboratory, Carnegie Institution of Washington 



INTRODUCTION 



Many igneous rocks contain inclusions of foreign material and 

 not infrequently these inclusions show evidence of having been 

 attacked by the magma, some to a moderate extent and others to 

 such an extent that only traces of the inclusion remain. To some 

 petrologists these inclusions are but the remnant of a great host, 

 most of which has been completely incorporated in the magma, and 

 to such incorporation or assimilation of foreign matter they would 

 assign the principal variations of igneous rocks. The variations are 

 not usually regarded by these petrologists as the result of assimila- 

 tion alone but of assimilation followed by the differentiation of the 

 syntectic magma which is supposed to have special powers of differ- 

 entiation not possessed by the original magma. Other petrologists 

 believe that magmas cannot be expected to have the energy content 

 necessary for the solution of a significant amount of foreign material; 

 that the amount of solution actually observed at and near contacts 

 is an approximate measure of the total and that the variations of 

 igneous rocks are quite independent of these slight additions, being 

 due to spontaneous powers of differentiation possessed by original, 

 uncontaminated magmas. 



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