CLASSIFICATION OF IGNEOUS ROCKS 561 
other. The proper course is to create new terms for new or dis- 
tinct conceptions, and not use one technical word in two or more 
quite different ways. To do so is as though some one should call 
all mammals marsupials, because he prefers the word marsupial; 
or should call all predaceous birds owls, because it is a short, con- 
venient word. Since short, comprehensive terms are needed for 
modal feldspathic minerals, and for modal ferromagnesian minerals, 
and for rocks made up predominantly of these groups of minerals, 
we suggest the term felsic for the group of modal feldspars, feld- 
spathoids, and quartz, and the term mafic for the group of modal 
ferromagnesian minerals of all kinds. The term femag has been 
used recently by Johannsen" for ferromagnesian minerals, but it 
appears to us to be objectionable both in form and in sound. 
tA. Johannsen. Jour. Geol., XTX (1911), 319. 
