234 Wisconsin Academy of JScieyices, Arts, and Letters. 



ON A PEOPOSED SYSTEM OF LITHOLOOICAL NO- 

 MENCLATURE. 



By T. C. Chamberlin, Ph. D,, Director of the Wisconsin Geological Survey. 



That our present system of lithological nomenclature is in some 

 important respects unsatisfactory, it is needless to assert. It is 

 inadequate, in that it falls far short of properly designating all 

 the mineral aggregates that have now become subjects of descrip- 

 tion, and of not infrequent reference in geological literature. It 

 is ambiguous, in that certain terms in common use are differently 

 used by different writers. So comrAon a term as syenite, and the 

 not infrequent ones melap'hyr and gahhro, are striking examples. 

 It is inaccurate, in that it groups under the same term, rocks 

 whose ultimate chemical composition varies widely, or those 

 •whose origin is diverse. It is mischievous, in that the individu- 

 ality of its naming inevitably implies hard and fast lines which 

 do not exist in nature. It is etymologically objectionable, in that 

 terms are wrested from their derivative sense, and forced into in- 

 congruous applications. Thus the term granite is driven from its 

 popular, and, as it happens in this case, proper application to a 

 wide class of grained crystalline rocks, and restricted to a certain 

 mineralogical aggregation. 



That these objections are felt in greater or less degree is shown 

 (1) by the drift in the signification of terms, (2) by the efforts 

 made to restrict and define old terms, (3) by the introduction of 

 new terms, (4) hy the compounding of terms, and (5) hy the use 

 of 'mineralogical names as defining adjectives. As examples of 

 compounding may be cited such terms as quartz-syenite, oligo- 

 clase-trachyte, quartz-augite-andesite, labradorite-diorite, horn- 

 blend-andesite, dioritic-gniess, hornblendic-biotite-gneiss, and so 

 on through the long list of complex te'rms that characterize the 

 later and more precise lithological discussions. 



The essential features of the proposed system lie in the direc- 

 tion of this manifest tendency, and consist, essentially (1), in an 



