304 H. Stank.// Jerom — Nomenclature of Igneous Rocks. 



II. — A Systematic Nomenclature for Igneous Eooks. 



By H. Stanley Jevons, M.A., F.G.S., 

 Assistant Demonstrator in Petrology in the Woodwardian Museum, Cambridge. 



I. Introductory. 



rriHE present nomenclature of igneous rocks is generally ac- 

 JL knowledged to be unsatisfactory, for not only is it without 

 useful meaning, but it is also so unsystematic that it forms a severe 

 tax upon the memory. The manifest and urgent need of reform, 

 which these circumstances create, must be my excuse for presenting 

 in a short note a suggestion likely to require much elaboration. 

 A systematic nomenclature, I need hardly say, can only rest upon 

 a systematic classification, so that the proposals I shall herewith 

 make would have been fitly accompanied by an attempt at producing 

 a classification of the kind. As I have found, however, that much 

 expenditure of time and labour will be necessary to accomplish this 

 task, I have decided upon publishing at once certain proposals with 

 regard to nomenclature, which could be largely applied to classifi- 

 cations at present in use. 



It has long been the custom of many authors to name subdivisions 

 of groups by prefixing to the family -name the name of the mineral 

 which distinguishes the subdivision.^ Thus we have, for instance, 

 muscovite-granites, hiotite-granites, hornblende-granites, and augite- 

 granites ; also hornblende-biotite-granites, augite-biotite-graniies, etc. 

 This system is undoubtedly a step in the right direction, because the 

 name of a sub-group is thus made to point out the distinguishing 

 feature in its composition. When more than one prefix is required, 

 however, such names become too cumbrous for general use, and the 

 practical result is that in such cases a new name is invented, 

 generally signifying nothing but the locality where the rock was 

 first found, or the name of its discoverer. The method breaks down, 

 in fact, under a severe test. 



II. Description of Prefixes. 



The system of nomenclature which I propose is based upon that 

 just described, but difi'ers from it in that the prefixes are contracted. 

 Several can be used, therefore, before a name tends to exceed 

 a reasonable number of syllables in length. Instead of hornblende- 

 biotite-granite, for instance, I should say Tiornbi-granite, pronouncing 

 the &i-syllable long, as in ' biotite.' 



Other advantages have been secured by the use of conventions as 

 to the arrangement of the prefixes, and as to the exact meaning of 

 the family-names. The order of the prefixes denotes the relative 

 abundance of the minerals, that of the most abundant standing next 

 to the family-name. Thus in a Jiornbi-granite biotite preponderates 

 over hornblende, whilst in a biJiorn-granite the reverse is the case. 



^ I use the term family throughout in the sense in which it is used by Rosenbusch 

 in his " Elemente der Gesteinslehre," that is to say, for groups like the granites, 

 diorites, etc. 



