40 



ALBERT JOHANNSEN 



therefore, each order represents an increased amount of the "ores" 

 (Fig. 5). The division points, as in the other case, are 0-5-50- 

 95-100. 



Order 1 



Foxdg 



Fig. 3. — Subdivisions of the tetra- 

 hedron into orders. 



Olivine 



Folds 



Fig. 4. — Family divisions in Classes 

 I to 3. 



Families.— Ym^Wy, each order is subdivided into famihes. In 

 Classes i, 2, and 3, the divisions, as shown in Figure 4, are at a-5-35- 

 65~9S~ioo on the feld- 

 spar base Hne, and at 

 0-5-50-95-100 from this 

 line up or down toward 

 quartz or the feldspath- 

 oids. Famihes o, i, 6, 

 II, 16, 21, 26, and 31 

 occur only once in each 

 class (cf. Fig. 3), since 

 the amount of plagio- 

 clase in each, whether 

 it be albite, acid plagio- 

 clase, basic plagioclase, or anorthite, is too small to make an 

 essential difference in the rock. These "hinge famihes" are classed, 

 for convenience, in Order i. 



Ores" 



Pyroxenes 

 Fig. s.— Orders and families in Class 4 



