CHEMICOMINERAL RELATIONSHIPS IN ROCKS 237 



such as phosphorus, titanium, zirconium, sulphur, chlorine, fluor- 

 ine, boron, etc., and their influence in modifying the proportions 

 of the preponderant minerals is self-evident. 



The discussion has been far from complete, but it is hoped 

 that it may lead to a better understanding of the relations 

 between the chemical and mineral composition of igneous rocks, 

 especially the factors controlling the range of quartz on the one 

 hand and of leucite and nephelite on the other. It certainly 

 makes more evident the interdependence of the various minerals 

 on one another and on the chemical composition of the magma. 

 And it may possibly suggest lines of investigation that may con- 

 tribute more substantially to our knowledge and conception of 

 these intricate relationships. Joseph P. Iddings. 



