THE BEHAVIOR OF INCLUSIONS IN IGNEOUS MAGMAS 541 



In the foregoing discussion granitic magma has been taken 

 merely as an example to which the principles developed may be 

 applied. As a further example it may be pointed out that saturated 

 dioritic magma cannot dissolve inclusions of gabbro, peridotite or 

 pyroxenite but, given the opportunity, it will react with those 

 inclusions and convert them into the hornblende and the plagioclase 

 with which it is saturated, at the same time precipitating a further 

 amount of this hornblende and plagioclase from its own substance. 



These are but examples of the application of the principle that a 

 saturated magma cannot dissolve inclusions of material farther 

 back in the reaction series (in general more basic) than the crystals 

 with which it is saturated. At the same time the magma can attack 

 these inclusions, reacting with them in such a manner as to convert 

 them into the crystals with which it is saturated. 



The dioritic magma we have considered will not remain indiffer- 

 ent to inclusions even of the exact composition of the crystals with 

 which it is in equilibrium, for as the temperature falls it will modify 

 the composition of these inclusions just as it modifies the composi- 

 tion of its own crystals. Indeed this case may be regarded as a 

 special case of that just discussed, for, as the temperature falls, the 

 composition of the liquid changes, and the inclusions then pass into 

 the class of those considered above. 



We now come to the case of inclusions of material later in the 

 reaction series than the crystals with which the liquid is saturated. 

 It should be noted that this includes masses of rock of the same com- 

 position as the liquid itself, for example its own chilled border phase. 



Saturated basaltic magma can react with inclusions of igneous 

 rocks later in the reaction series (in general more acid) in such a way 

 that the inclusions become part of the liquid, crystals of the phases 

 with which the basalt is saturated being precipitated at the same 

 time. If these crystals are removed by gravity or otherwise the 

 action on the inclusions may continue, the liquid changing in com- 

 position toward the composition of the inclusions and precipitating 

 later and later members of the reaction series until finally it is satu- 

 rated with precisely the crystalline phases contained in the inclu- 

 sions. If granitic inclusions, say, were available at the upper 

 contact of a mass of basaltic magma, they would be attacked by the 



