146 CARNEGIE INSTITUTION OF WASHINGTON. 



of reactive solution, the heat of solution of inclusions being supplied by the 

 precipitation of their heat equivalent of the member of the series with which 

 the liquid is saturated. It should be noted that the material that can by 

 this reactive process become a part of the liquid must consist of a later member 

 of the reaction series, that is, must be material toward which the liquid could 

 pass spontaneously bj^ fractional crystallization. The net effect upon the 

 liquid is, then, to push it onward upon its normal course. 



The products of crystallization of subalkaline magmas can be arranged 

 as reaction series. The action of magmas upon foreign inclusions of igneous 

 origin may be deduced from this arrangement of the crystalline products as 

 series by application of the principles developed from the above study of 

 simple systems. Thus we find that a granitic magma saturated with biotite 

 can not dissolve olivine, pyroxene, or amphibole, but can only react with 

 them to convert them into biotite, the phase with which it is saturated; or, 

 stated more generally, no saturated magma can dissolve inclusions consisting 

 of minerals belonging to an earlier stage of the reaction series (usually more 

 basic). 



Saturated basic magma, on the other hand, will react with inclusions 

 belonging to a later stage of the reaction series (more acidic), the reaction 

 being of such a nature that the inclusions become a part of the liquid by 

 precipitating their heat equivalent of the phases with which the magma is 

 saturated (basic minerals). The inclusions, it should be noted, must be of a 

 composition toward which the liquid could pass spontaneously by fractional 

 crystallization. Thus, saturated basaltic magma can dissolve granitic in- 

 clusions by precipitating basic minerals, and the granitic material passing 

 into solution then becomes a contribution to the normal granitic differentiate 

 that may form by fractional crystallization if the conditions are appropriate. 



The behavior of inclusions of sedimentary origin is more complicated, since 

 sedimentary material does not belong in the reaction series. A consideration 

 of the extent and nature of the variation of composition possible in the crys- 

 talline phases formed from a magma shows that the incorporation of consider- 

 able amounts of sedimentary material would ordinarily bring about merely 

 an adjustment in the composition and relative proportions of existing phases. 

 As a result of the non-appearance of new phases, the general course of frac- 

 tional crystallization is unaffected. In general, the adjustment noted takes 

 place through precipitation of the phases with which the magma is saturated. 

 As an example, it may be stated that the addition of highly aluminous sedi- 

 ments to basic magma should bring about the formation of anorthite and 

 enstatite molecules at the expense of diopside molecules and should therefore 

 cause the precipitation of crystals rich in anorthite and enstatite. Such 

 action may have been important in the formation of many norites. The 

 foreign material becomes a part of the general mass as a result of reaction and 

 precipitation rather than by simple solution. 



It may be stated, therefore, that magmas may incorporate considerable 

 quantities of foreign inclusions, both by the method of reactive solution and 

 by reactive precipitation, and such action may have been important in con- 

 nection with the production of certain individual masses. Thus some norites 

 may have been produced as a result of the reactions discussed above, some 

 granites may have had their mass augmented by reactive solution of granitic 

 inclusions in the magma from which they differentiated, some alkaline rocks 

 may have been formed as a result of the presence of limestone inclusions in 

 the liquid from which they differentiated. All of these actions are, however, 

 an emphasizing of normal processes possible in the absence of foreign matter. 

 It is doubtful whether the presence of foreign matter is essential to the pro- 

 duction of any particular type of differentiate. 



