542 N. L. BOWEN 



magma in the manner noted and, in a lower layer, accumulation of 

 the precipitated products of the reaction would take place. These 

 would be the early crystals formed in basaltic magma. The upper 

 liquid is thus gradually changed in composition and the crystals 

 precipitated from it are successively later and later members of the 

 reaction series. Attack upon the inclusions continues until finally 

 the upper liquid becomes granitic. All of this depends on a rate of 

 cooling slow enough for free crystal settling to occur. But if the 

 cooling is sufficiently slow for crystal settling all of these results 

 could accrue from the simple differentiation of the basaltic magma. 

 Indeed the principles developed show that the inclusions can become 

 part of the liquid only when they have a composition toward which 

 the composition of the liquid can vary by spontaneous differentia- 

 tion. 



Nevertheless it is apparent that the amount of granitic differen- 

 tiate might be greatly augmented by this action. It may safely be 

 assumed therefore that in many individual cases considerable quan- 

 titative importance in the production of a granitic differentiate of 

 basic magma is to be assigned to the action noted. It is a sort of 

 solution of granitic inclusions though not a simple, direct solution 

 and is in no sense essential to the production of a granitic differen- 

 tiate. 



Daly is of the opinion that many granites are secondary, that is, 

 are formed by solution of granite in basaltic magma and subsequent 

 differentiation.' It is seen from the above that theoretical consider- 

 ations support belief in a process which, in its results at least, is 

 practically that advocated by Daly. The process itself he considers 

 to be rather a simple solution of granite in superheated basaltic 

 magma. We have seen that no superheat is necessary to produce 

 solution by a sort of reactive process. Moreover, we have seen that 

 the incorporated granitic material is to be regarded rather as a 

 contribution to the normal granitic differentiate. There appears, 

 however, to be no reason to doubt that, at times, this contribution 

 might equal or possibly even exceed in amount the granitic differ- 

 entiate capable of formation from the uncontaminated magma. 



' Indeed, Daly derives in this manner all granites except a supposed original 

 granitic shell of the earth {Igneous Rocks and Their Origin, p. 323). 



