624 FRANK F. GROUT 
of salic minerals, as far as the classification is commonly used. In 
the subrang Auvergnose the diagram shows that the prominent 
femic mineral may be either diopside, hypersthene, or olivine. 
For this reason the diagrams of salfemane subrangs may show a 
great deal of variation in the femic minerals. However, if the 
Fic. 2.—A multiple diagram of a series of rocks from the Harzose subrang in the 
quantitative classification. The quartz and feldspars are predominant here also, 
but the more siliceous minerals here give way to increased amounts of anorthite. 
classification is carried one step farther, to the “grad,” these 
varying rocks would fall in different grads. As a whole it is clear 
that analyses of a single group in the quantitative classification 
show their relationship conspicuously in the diagram. 
Attention may also be called to the contrasting series shown in 
the diagrams of “A Type of Igneous Differentiation.” The 
variation in the gabbro series at Duluth shows no tendency to 
develop a type intermediate between the gabbro and the red rock. 
The second picture, the red rock, seems to be a strikingly different 
class of rocks. 
