THE 



JOURNAL OF GEOLOGY 



SEPTEMBER-OCTOBER, 1002 



A QUANTITATIVE CHEMICO-MINERALOGICAL 

 CLASSIFICATION AND NOMENCLATURE OF 

 IGNEOUS ROCKS. 



CONTENTS. 



SUMMARY. 



PART I. CLASSIFICATION. 



Introduction. 



Defects of present system. 



Basis of classification. 



The facts to be considered ; The existence of petrographic provinces ; The 

 principles ; A brief discussion of various principles. 



Cheinico-7nineralogical classification. 

 Standard mineral composition. 



Construction of the system. 



Outline of the system. 



Class; Subclass; Order; Suborder; Rang; Subrang; Grad ; Subgrad ; 

 Section. 



The role of actual mineral composition and texture in rock classification. 

 Actual mineral composition. 



Complete or almost complete accord between the mode and norm; Appreci- 

 able difference between norm and mode ; Varieties ; Indeterminable modes. 

 Texture. 

 Crystallinity ; Granularity ; Fabric ; Heterogeneous textures. 



PART II. NOMENCLATURE. 



Magma tic names. 



Termination ; Root ; Names. 

 Rock names. 



Actual mineral composition ; Texture ; Examples of names ; Type and habit. 

 Rock names for general field use. 



Phanerites ; Aphanites ; Glasses. 

 Vol. X, No. 6. 555 



