MINERALOGICAL CLASSIFICATION OF IGNEOUS ROCKS 89 



sodic-diorite, calcic-diorite, and anorthite- (or lime-) diorite. As 

 a matter of fact, these rocks in the^old classification have special 

 names, namely, soda-syenite, diorite, gabbro, and anorthite-gabbro, 

 and, except the first, which more properly is an albite- (or soda-) 

 diorite, should not be changed. The prefixes persodic, dosodic, 

 etc., of the C.I.P.W. system cannot be used, since they apply to 

 definite proportions of the constituents and not to those used here. 



FAMILY NAMES 



It is not the intention in this paper to name definitely all the 

 families, those in Figs. 24 to 27 being given simply as examples. 

 Most of the family names have been determined, and will be given in 

 a succeeding paper. The family name should be that of a rock with- 

 out abnormal constituents which occupies nearly the center-point of 

 that family. Thus a garnet-bearing rock should not be chosen as a 

 family representative if a non-garnetiferous rock is known, the 

 garnetiferous rock being indicated by a prefix. The name should 

 also be that of the plutonic rock, if such is known. Furthermore, 

 if only one name is given to the rocks of the same family in the 

 various classes, it should be given to Class 2; Class 1 will then be 

 its leucocratic variety and Class 3 its melanocratic variety. It is 

 not to be understood from this that the writer thinks it undesirable 

 to name particular varieties, for it may be very desirable if they 

 represent distinct types and if their relationships to known rocks 

 are clearly shown; but if a new type differs only by the presence 

 of a single abnormal constituent, that constituent should simply 

 be used as a modifying name. 



The reasons for using certain family names, such as adamellite 

 for quartz-monzonite, tonalite for quartz-diorite, etc., will be given 

 in a succeeding paper. Syenodiorite, syenogabbro, and grano- 

 gabbro are introduced as new terms to fill definite positions, the 

 last being the orthoclase-bearing variety of quartz-gabbro and 

 analogous to granodiorite, the first two being the quartz-free 

 varieties of granodiorite and granogabbro. 



Sub-families in Orders 1, 2, and 3 are formed on the basis of the 

 predominating dark or auxiliary constituent; thus under granite 

 are the divisions biotite-granite, hornblende-granite, topaz-granite, 



