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PROCEEDINGS OF THE AMERICAN ACADEMY. 



common association of granites (and liparites) with andesites (and 

 diorites) in nature. The question is open as to whether the primitive 

 granite-liparite magma was not a polar differentiate of an andesitic 

 magma, preferably by a settling-out of the phenocrystic constituents 

 (in solid or liquid phases) from the andesitic magma. 



Other related questions are raised by the comparison of the mean of 

 average granite and average basalt with average diorite (including 

 quartz diorite). 



Is basalt the basic pole, granite the acid pole, of a primitive differ- 

 entiation of diorite magma? Is diorite the product of mixture of 

 primitive, granitic crust and primary basalt still molten beneath? 

 Though the averages give no answer, they tend to keep these funda- 

 mental queries before the eye of the petrologist. 



4. The averages have been arranged so as generally to place 



