H. Stanley Jevons — Nomenclature of Igneous Roclcs. 307 



of the gabbro family, no account being taken of the usual accessories. 

 Reference to the table (No. IV) on p. 312 will show that this prefix 

 occurs again in the descriptive name for umptekite, namely monampli- 

 -alisyenite. It is used here because, whilst in certain members of the 

 family an amphibolo is the most abundant ferromagnesian mineral, 

 in umptekite it is the only one, and to avoid all risk of confusion it is 

 well to state that fact in the name. The use of this prefix is really 

 simply a means of avoiding the use of the same name in both an 

 extended and restricted sense at once. 



V. Order of Prefixes. 



The order in which prefixes of different kinds are placed when 

 required in the same name is an important matter. The rule which 

 I propose is that a prefix used to name a major subdivision be 

 always placed nearer to the family name than a prefix used for 

 a minor subdivision. For instance, supposing that the subdivisions 

 of the dolerite family, founded on mineral composition in the 

 ordinary way, were themselves subdivided according to structure, 

 then the structure prefix would always precede the mineral prefix 

 in the name of each of the ultimate subdivisions, producing such 

 names as ophit-oli-dolerite, hypidio-horn-dolerite, etc. When on the 

 other hand the first subdivision is on the basis of structure, as in 

 the rhyolites, the order must be reversed, producing such names as 

 diopsi-mipegmo-rhyolite, bi-perlo-rhyolite, etc. This rule is obviously 

 the most convenient, for it leaves the name of a major subdivision 

 intact in the names of the minor subdivisions which it contains, 

 so that a single glance shows to which major subdivision any minor 

 subdivision belongs. It must not be supposed that this double 

 subdivision and the cumbrous names it produces will be frequently 

 employed. It is probable, however, that as the study of igneous 

 rocks progresses, subdivision will be carried further and further ; 

 and it is therefore well to be prepared beforehand with a method 

 for naming sub-groups of future origin in any system of nomen- 

 clature which we adopt to-day. 



It will have been observed that hyphens are always placed 

 between prefixes of different kinds, and between a prefix and the 

 family-name, in order to facilitate reading the compound name. 

 They are not required to separate prefixes of the same kind, as for 

 instance when a series of mineral prefixes follow one another, nor 

 should they be inserted within family- or subfamily-names. 



VI. Lists of Contractions. 



The various kinds of prefixes have now been fully discussed. 

 For the sake of uniformity, in case others should wish to use this 

 system, I proceed to display in full all the contractions which 

 appear likely to be necessary. The first list, containing the 

 contractions of mineral names, includes, I believe, all that are 

 likely to be required. It will be noticed that different forms are 

 generally needed according to whether the next syllable begins with 

 a vowel or a consonant. 



