530 N. L. BOWEN 



kind that the liquid should be enriched in the constituents toward 

 the low temperature end of a solid solution series and the solid in 

 those toward the high temperature end. 



We have seen, then, that even when we add inclusions of a plagio- 

 clase of the same composition as the plagioclase existing as liquid 

 in the magma, quite marked reaction effects may be found. 



Let us now examine the same example but make the cooling of 

 the liquid very slow. In other words, we shall discuss the end result 

 of the action described above, which gives a reaction rim only as a 

 temporary condition. In this case we shall imagine that the liquid 

 formed about the inclusion becomes a part of the main mass of 

 liquid as a result of diffusion and convection, and also that the solid 

 products of the reaction become distributed through the liquid upon 

 disintegration of the inclusion, due to the formation of local pockets 

 of liquid and to the volume changes taking place in the change of 

 composition of the solid phase. Thus the inclusion completely dis- 

 appears as a distinct entity. Let us imagine that the amount of the 

 inclusions wg-s lo per cent of the total and determine what the effect 

 on the mass as a whole will be. The bulk composition of the mass 

 is represented by the point K and if the temperature were main- 

 tained at 1250° the inclusions, formerly AbjAui, would be changed 

 to crystals of a composition close to AbiAn4 and the liquid would 

 acquire the composition P. The crystals would amount to only 

 about 6 per cent of the mass and to maintain the temperature con- 

 stant would require addition of heat. If the only heat available 

 were that of the mass itself its temperature would be lowered and a 

 slightly greater amount of crystals formed. The net result would 

 be, however, a marked change in the composition of the inclusions, 

 a moderate decrease in the actual amount of solid material with 

 corresponding increase in the amount of liquid. The liquid, too, 

 becomes more albitic, that is, is pushed onward upon its normal 

 crystallization course. 



If, instead of inclusions of AbjAui, more sodic inclusions were 

 added, say AbaAni, there would be a somewhat greater increase in 

 the amount of liquid and a markedly greater enrichment of the 

 liquid in more albitic plagioclase. Inclusions as rich in albite as 

 AbioAni might be completely melted by the liquid before becoming 



