CLASSIFICATION OF IGNEOUS ROCKS 231 



227 is granodiorite as originally intended by Lindgren (p. 168 

 above) with the Kf-Plag ratio 50-50 to 5-95. (Family 237 is 

 granogabbro.) 



221 1 is normal syenodiorite (23 11 syenogabbro) with Kf-Plag 

 ratio like the preceding. 



For those who wish to use the monzonitic subfamilies : 



226' is more limited granite with the Kf-Plag ratio between 

 95-5 and 65-35. It may be called monzogranite. 



2210' is limited syenite with the same Kf-Plag ratios. It may 

 be called monzosyenite. 



226-7' is quartz-monzonite or adamelhte, Kf-Plag ratios 65-35 

 to 35-65. 



22io'-22ii' is monzonite, with same ratios as preceding. 



227' is limited granodiorite with Kf-Plag ratios between 35-65 

 and 5-95. Better called monzotonalite, leaving granodiorite for 227. 



22 11' is monzodiorite, same ratios as preceding. 



Thus petrographers who wish to use quartz-monzonite and 

 monzonite have subfamilies at their disposal and these subfamilies 

 may be carried through the whole system if desired. Normally 

 only the families would be used. 



So far as names are concerned, they remain as given in the 

 preceding article except that Families 3, 8, 13, 18, 23, and 28 

 drop out entirely and the adjacent families (and their names) extend 

 to the center Hne. 



In Class 4 the subdivisions are to be made on the same divi- 

 sions, therefore the left face of Figure 5 should be divided as the 

 upper half of Figure 7 and the positions computed in the same 

 manner as the families in the other classes. 



In Part I, therefore, the following changes are to be made in 

 the rules on pages 43 and 44. 



Page 43, 3 lines from bottom, omit five. 



Page 44, lines l-?>,Jor 0-5-35-65-95-100 read 0-5-50-95-100. 



Page 44, lines 12-14, for the mineral of one corner, etc., to end of sen- 

 tence, read olivine to the sum of the biopyriboles, and of biotite plus amphi- 

 bole to pyroxene. 



Another correction that should be made is on page 42, where zinnwaldite 

 is to be taken away from the auxiliary constituents and added to the dark 

 micas under mafites. 



