THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 523 



certain amount of superheat, the first few inclusions added would 

 receive the full benefit of it and might be fused, but the magma would 

 suffer a correspondingly marked loss of heat. In other words, the 

 net result of the addition of an amount sufficient to produce a signifi- 

 cant change of composition, say 10 per cent, would be the same even 

 though they were added slowly and the first additions were drasti- 

 cally affected. Not only do magmas commonly fail to convert inclu- 

 sions into liquid but they also fail to effect such changes as the 

 transformation of quartz into tridymite and of wollastonite into 

 pseudo-wollastonite, which fact must be regarded as indisputable 

 evidence of the prevailing low temperatures. 



There seems no reason, therefore, to doubt that direct solution 

 of foreign material in superheated magmas cannot be a factor of 

 importance in petrogenesis. However, the importance of superheat 

 has been greatly exaggerated both by those who adhere to the view 

 that magmas dissolve large quantities of foreign matter and by 

 those who deny it. We shall find in the sequel that even saturated 

 magmas may produce very marked eft"ects in the way of incorpora- 

 tion of foreign material. 



EQUILIBRIUM EFFECTS BETWEEN "INCLUSIONS" AND LIQUIDS 

 IN INVESTIGATED SYSTEMS 



In the following discussion of the effects of liquids upon inclu- 

 sions, whose composition is embraced within investigated systems, 

 attention will be confined, unless otherwise stated, to saturated 

 liquids. This is done because we have found in the foregoing dis- 

 cussion that the superheated condition has little importance in 

 nature. But lest it be thought that this is going too far in the way 

 of eliminating superheat we have made another assumption that 

 should amply compensate, namely, that the inclusions are already 

 heated to the temperature of the liquid before immersion in it. 



It is proposed to discuss the magnitude of the heat effects 

 involved when reactions go on between solid inclusions and liquid 

 in systems that have been experimentally investigated and where 

 the equilibrium relations at various temperatures and the approxi- 

 mate heat effects are known. It is not expected that the numerical 

 results so obtained will have any direct applicability to natural 



