REPORT OF TEE CHIEF ASTRONOMER xix 



SESSIONAL PAPER No. 25a 



Page. 



Average ratio of calcium to magnesium in the limestones of the 



different periods. , 664 



Origin of certain iron ores, cherts, and jaspers 669 



Origin of the petroleum and natural gas emanating from pre- 



Cambrian sediments 669 



Direct evidence of the chemical precipitation of the carbonate rocks 



in the Priest river and Belt-Cambrian terranes 670 



Summary 672 



Premises 672 



Conclusions 673 



CHAPTER XXTV. 



Introduction to the theory of igneous rocks 6j77 



Classification of the igneous rocks 677 



Average compositions of leading types 679 



Average specific gravities of certain types 696 



Source of magmatic heat 696 



Composition of the substratum; the general earth-magma 699 



Primary acid shell of the earth 702 



Abyssal injection of magma 705 



Origin of volcanic action 707 



CHAPTER XXV. 



Classification of igneous intrusive bodies 715 



Introduction 715 



Principles of classification 715 



Injected bodies 716 



Dike 716 



Intrusive sheet 717 



Laccolith 717 



Phacolith 718 



Bysmalith 719 



Volcanic neck , 719 



Chonolith 719 



Ethmolith 720 



Subjacent bodies 720 



Boss 720 



Stock 721 



Batholith 721 



Proposed classification 722 



8364— C 



