428 N. L. BOWEN 



Throughout a long period this liquid is therefore more or less free 

 to escape into the surrounding rocks, where it is used up in pro- 

 ducing metasomatic reactions of various kinds. The materials of 

 this liquid may therefore be frequently, perhaps normally, unrepre- 

 sented in the igneous sequence for this very reason. Foye has 

 brought forward quantitative evidence of the introduction of alka- 

 line material in great quantity from granitic magma. Following 

 Daly he imagines that these alkaline liquids have been produced by 

 reaction between limestone and granite, but it is not at all clear 

 how this can be considered to apply to the particular case under 

 discussion. In its original form the limestone-syntectic hypothesis 

 was rather simple, and, as the writer has stated elsewhere, it 

 assumed rather likely reactions. The most important reaction was 

 the taking of silica by the lime to form lime silicates, the free silica 

 being used up first and later some of the silica of feldspar molecules 

 with consequent production of feldspathoids. However, it is 

 imagined in this particular case that limestone reacts with granitic 

 magma but does not desilicate it, in fact leaves it still a granitic 

 magma, and yet reacts in such a way as to produce large amounts 

 of alkaline liquors, of which part are introduced into the invaded 

 limestones and part crystallize with formation of nephelite syenite. 

 The manner in which this can occur is by no means so easily 

 followed. On the other hand, it appears to afford a natural explana- 

 tion if it is supposed that biotite granite magma is normally capable 

 of supplying this alkaline liquid, and that it is produced by reactions 

 of which we have direct evidence in the granite itself. The liquid 

 may be used up by introduction into surrounding rocks or by partial 

 reversal of these reactions if it remains in the interstices of the 

 granite. On the other hand, if it is separated from the granite in 

 such a way as to form a distinct liquid it will give rise to a mass of 

 nephelite syenite and may indeed further differentiate to give 

 derivatives of nephelite syenite. 



In the paper in which this mode of origin of nephelite syenite 

 was proposed it was stated that a continuance of the process of 

 settling of crystals could produce nephelite syenite from granite in 

 the same manner as granite itself may be produced from gabbro. 

 This manner of separation of the liquid from the crystals is not 

 now considered likely, indeed the essential reactions have probably 



