xx DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 



CHAPTEE XXVI. 



Page. 



Mechanism of batholithic intrusion. . . . 725 



Field relations 725 



Time relations 729 



Chemical relations 729 



Theories of batholithic intrusion 730 



' Laccolithic ' hypothesis . . 730 



' Marginal assimilation ' hypothesis 731 



Hypothesis of ' magmatic stoping ' 734 



Magmatic shattering by differential thermal expansion 735 



Relative densities of magma and xenolith 740 



Influence of plutonic pressures on rock density 744 



Sinking of the shattered blocks 745 



Rise of magma through stoping 747 



Testimony of laccoliths 747 



Problem of the cover 748 



Supply of the necessary heat; magmatic superheat and its causes 750 

 Capacity of superheated, plutonic magma for melting and dissolv- 

 ing xenoliths 752 



Objection founded on rarity of evidences of assimilation at ob- 

 served wall-rocks 754 



Abyssal assimilation 755 



Existence of basic stocks and batholiths 757 



Differentiation of the syntectic magma 759 



Origin of granite; the petrogenic cycle 760 



Eruptive sequence 762 



Origin of magmatic water and gases 763 



General remarks on the stoping hypothesis 766 



CHAPTER XXVII. 



Magmatic differentiation 769 



Preliminary note 769 



Relation to crystallization 769 



Limited miscibility 770 



Gravitative differentiation 771 



Origin of basic contact-shells 772 



Chemical contrast of plutonic and corresponding effusive type 774 



Expulsion of residual magma 776 



Effect of solution of foreign rock 776 



CHAPTER XXVIII. 



General theory of the igneous rocks and its application. . 777 



Condensed statement of a general theory 777 



