CLASSIFICA TION OF IGNEOUS ROCKS 623 



h) As far as possible localities whose rocks occur near the 

 classificatory borders of a given group are to be avoided. 



Intermediate magmatic names. — A rock, whose composition is 

 such that its magma occurs so near the border line of any divi- 

 sion of the system as to be considered a transition magma, 

 receives a compound magma name, made by uniting the names 

 of the two divisions concerned, and connecting them with a 

 hyphen. The name of the division in which the rock occurs is 

 to be preceded by that of the neighboring division. 



Names. — As the Classes are few in number the strictly mne- 

 monic method of root-formation is applicable to them, and we 

 have accordingly named them on the basis of the relative 

 amounts of the standard salic and femic minerals present, these 

 being indicated by the syllables sal and fern, as already explained. 

 The relative amounts are shown by the prefixes per- and do-, 

 which stand respectively for extremely abimdant and domi?ia?it. 

 The names for the five classes are as follows : 



-r. ! x- n Sal 7 



1. rersalane : Extremely salic — — — >- . 



Fem 1 



2. Dosalane : Dominantly salic— — — <-> — . 



J Fem 1 3 



Sal s x 



3. Salfemane : Equally salic and femic — — — <->•—. 



Fem 3 5 



4. Dofemane : Dominantly femic — — — <->- . 



J Fem 5 7 



Sal 1 

 k. Perfemane : Extremely femic — — — < - . 

 J Fem 7 



For other magma units names derived from geographical 

 localities have been used, as already explained. Those sug- 

 gested by us apply to the more important divisions of the sys- 

 tem, and to those based on the best established data, derived 

 from the collection of several thousand analyses already referred 

 to, and from older analyses where available. There are numer- 

 ous divisions for which we have not sufficient data to warrant 

 our suggesting names at this time. Owing to the large number 

 of names selected, they are presented in tabulated form, in such 

 manner that they can be understood without difficulty. 



