696 C. R. VAN HISE 
in a number o finstances precisely as proposed, for discriminat- 
ing rocks. For example, he describes /elleforsdiabas, aasby- 
diabas, sarnadiabas, ottfjallsdiabas.* Had some _ petrographers 
described these rocks perhaps we would have had four additional, 
independent names to remember, the value of which we would 
know absolutely nothing of, without any suggestion whatever as 
to the family, in Rosenbusch’s sense, to which these new rocks 
belong. 
The method proposed has unconsciously been followed to 
some extent, by the’ United “States |Geolopgical’ Survey that 
organization has recognized that a sufficient number of inde- 
pendent names could not and should not be coined to designate 
every variety of rock. It has practically, if not by definition, 
recognized the endless variation and gradation throughout rock 
formations, by providing that aqueous and metamorphic formations 
alike should be given local names; for example, Chicopee-shale, 
Floosac-scehist), Becket-sneiss, eter.) Unis use of local eimamies 
has furnished a more accurate method of discrimination than 
could be afforded by independent names. Moreover, only rocks 
which are present in some quantity have been given formation 
names. Thus, by practice at least, the idea of abundance as a 
factor in the naming of rocks has been recognized. 
Suggestion to petrographers who have introduced new names.—In 
this connection it may be suggested that petrographers who have 
recently introduced new independent names would perform a 
service to geologists who are not petrographers, and to many 
other petrographers, by giving in subsequent papers equivalent 
names on the basis of the plan above advocated, to the special 
rocks to which they have given names. If this be done, the 
relative merits of the two plans will be tested. Within a short 
time it will be seen whether geologists and petrographers use 
the independent names or the more general names compounded 
with geographical and mineralogical terms. Where a new inde- 
pendent name was really needed, and performs a service in the 
* Mikroskopische physiographie, II, Massige Gesteine, H. ROSENBUSCH; S. 219-220. 
? Holyoke folio No. 50, Geological Atlas of the United States. 
