528 



N. L. BOWEN 



If the rate of withdrawal of heat were very slow this reaction might 

 result in an actual rise of temperature and the establishment of 

 equilibrium at the higher temperature where the plagioclase crystals 

 would be slightly more calcic than AbiAn4. If the liquid A had 

 come into being as a result of the partial crystallization of another 

 liquid, and if it carried plagioclase crystals suspended in it that 

 showed zoning, the addition of the foreign inclusions mentioned 

 might therefore result in a reversal of the zoning. 



Fig. 6. — Equilibrium diagram of diopside, anorthite, and albite 



The "attack" of the liquid upon the inclusions would be facili- 

 tated at the margins and along any channels where the inclusion 

 happened to be more readily penetrated. The replacement of a 

 small unit of AbiAn,, by AbiAn4 means a large local increase of 

 volume so that the action is bound to have a disintegrating effect 

 upon an inclusion suspended in liquid. Thus the material of the 

 inclusion, as it is gradually made over, tends to become strewn about 

 in the surrounding liquid but there is no actual solution, no increase 

 in the amount of liquid — indeed, there is a diminution. Such should 

 be the behavior of an inclusion richer in calcic plagioclase than the 

 crystals with which the Uquid was in equilibrium. At a later point 



