560 W.CROSS, J. P. IDDINGS, L. V. PIRSSON, H. S. WASHINGTON 
definition, or others’ usage. Witness the frequent misuse of the 
chemical terms “acid”? and “basic”? as applied to the limesoda- 
feldspar series. Oligoclase is often said to be a more “acid”’ feld- 
spar than andesine, and labradorite a more “basic” one. It is 
not to be assumed that petrographers misusing these terms are 
wholly ignorant of chemistry. We, also, are petrographers and 
understand how we have done such things. We plead guilty to 
various degrees of indifference, lack of enterprise, and ignorance. 
The petrographical custom of redefining any rock name to suit 
individual preference and the resulting multiplicity of definitions 
is, no doubt, in part responsible for this common indifference to all 
technical terms, whether distinctively petrographic or derived 
from other sciences. In some cases, names of rocks and technical 
terms have been so vaguely defined in the first instance that there 
is latitude of judgment in their application and an invitation to 
improve their definition. But when the first definition of any 
term has been precise and clearly specific, its misuse and distortion 
are inexcusable. 
The terms salic and femic were applied definitely to certain 
minerals chosen to form norms of igneous rocks in the Quantitative 
System of Classification. They were applied strictly to calculated 
normative minerals: salic to normative quartz, feldspar, lenads, 
zircon, and corundum; femic to normative non-aluminous ferro- 
magnesian, and calcic pyroxenes, olivines, and other minerals 
specifically enumerated and described. It excluded aluminous 
pyroxenes, amphiboles, micas, etc., to which the term alferric was 
applied. 
Some petrographers have fancied the terms salic and femic 
as short words, which they wish to apply to modal quartz, feldspar, 
and feldspathoid minerals in one case, and to all modal ferro- 
magnesian minerals in the other. These terms have also been 
applied to major rock groups. Such applications are not proper 
uses of these terms, and introduce confusion where it can be easily 
avoided. 
Felsic and mafic.—Short expressions are useful in the general or 
qualitative description of rocks for the feldspathic minerals and 
quartz on the one hand, and for the ferromagnesian minerals on the 
