CLA SSIFICA TION OF IGNEO US ROCKS 6 1 9 



nated system, from the broadest to the smallest division. Each 

 separate division, from the largest to the smallest, should have a 

 distinctive appellation, precluding confusion with others, and 

 indicating at once its relative place in this system and its char- 

 acter. The names should be mnemonic, if possible, expressing 

 the idea to be conveyed, short, euphonious, and not liable to be 

 mistaken for one another. 



In accordance with the principles just stated, we have con- 

 structed names for the various magmatic divisions which have 

 been explained in the preceding pages on classification. In 

 addition to these it will be necessary to employ qualificatory 

 terms to express the variable characters of mineral composition 

 and texture, which, with the appropriate magmatic name, will 

 apply to the rocks themselves. The nomenclature, then, will be 

 to a certain extent polynomial. These qualifiers may be applied 

 at any point in the system. 



MAGMATIC NAMES. 



Termination. — It is possible to indicate the place of any 

 given rock name in a system by employing only one termination 

 and by varying the root of the word, which then alone indicates 

 at the same time both the character of the group and its relative 

 position in the system. Thus, with the single termination -ite 

 the family name, foyaite, expresses the concept of rocks formed 

 essentially of alkali-feldspar and nephelite, while smaller divi- 

 sions of this are indicated by such names as laurdalite, litchfield- 

 ite and lujavrite. 



But this method is very unsatisfactory and primitive, in that 

 it does not avail itself of the very powerful aid afforded by such 

 possible terminations as would in themselves give considerable 

 knowledge of the group named. Furthermore, while feasible 

 with a small number of names, such a method involves a great 

 tax on the memory, especially with the rapid growth of our 

 knowledge of rocks and of new rock types, and the necessity 

 for new names. 



These serious objections to the use of but one termination 



