550 N. L. BOW EN 



tion produces only the same solid phases slightly modified in com- 

 position. If consolidation took place under conditions permitting 

 fractionation by settling of crystals no fundamentally new differ- 

 entiation potentialities would be introduced by the solution or reac- 

 tion with foreign material that has been discussed. The magma 

 thus modified could give a diorite-granodiorite-granite sequence, 

 say, only if the original magma could also have done so under the 

 same conditions. It is a question whether, in the case of unsatu- 

 rated magma, it can be safely assumed that the degree of superheat 

 may be such that an amount of material can be dissolved in excess 

 of that which can be taken care of by the adjustments in composi- 

 tion of existent phases. If this is possible new phases will appear 

 and the course of crystallization and differentiation might be funda- 

 mentally modified. In the case of added CaO, for example, the new 

 phase melilite might appear and the differentiates formed might be 

 fundamentally different; might be, say, certain alkaline types as 

 Daly has postulated. 



EFFECTS OF BASALTIC MAGMA ON ALUMINOUS SEDIMENTS 



With this possible exception in the event of excessive superheat, 

 the statement should hold that reaction with foreign material can 

 produce no new differentiation potentialities in the magma. Yet it 

 is certain that some lines of differentiation may be emphasized by 

 such agency, that is, that certain types of differentiate should be 

 quantitatively of greater importance. This we have found to be 

 true of reaction of magma with previously solidified igneous material. 

 Thus when basaltic magma reacts with granitic material the tend- 

 ency is to increase the amount of granitic differentiate capable of 

 forming from the basalt. The effect of reaction with aluminous 

 sediments is of sufficient importance to justify further discussion at 

 this point. The result has been shown to be the emphasizing of 

 more magnesian pyroxene and of anorthite. Now under certain 

 conditions, not well understood, magnesian pryoxene separates from 

 magmas as a distinct phase, an orthopyroxene, and the addition of 

 aluminous sediments should emphasize this tendency. The forma- 

 tion of norite and of pyroxenites characterized by orthopyroxene as 

 differentiates from basaltic magma, may therefore be facilitated by 



