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G. W. Tyrrell—Petrographie Nomenclature. 495 
Considerable outcry has been made in the past by a conservative 
school of petrographers against the supposed enormous increase in 
the number of rock names, many of which are regarded by them as 
unnecessary. Yet, counting the names given in “Holmes” glossary, 
dating up to 1920, we find that only 428 igneous rocks have separate 
names (excluding compound terms built up with mineral qualifiers, 
which, however, do not ge in the list). Some of these are 
neatly or quite obsolete; others are redundant, or cover but a 
minute portion of the petrogr raphical field, or depend for their 
value on trivial differences that would not now be recognized as 
suitable bases for nomenclature. A great many of these names would 
certainly be discarded upon a critical revision. Probably less than 
half of the igneous rock names, or say about 200, are used at all 
frequently or with close definition, and are thus woven into the 
living texture of petrological science. Similarly there are only 
137 sedimentary and 104 metamorphic rock names, which are subject 
to the same considerations as are made in the case of igneous rocks. 
We may draw the conclusion that there are not too many rock 
names ; on the contrary, there are ridiculously few, especially when 
the subject is compared with sister natural history sciences. There 
are certainly insufficient names to cover the enormous field of 
rocks at all adequately, and petrography thus suffers from a 
deficiency rather than a plethora of names. ‘There are insufficient 
terms to indicate what are often considerable degrees of difference 
in rocks. Moreover, the terms in use are unequally distributed over 
the petrographical field ; in common types of rocks a great range 
of difference may be covered by single names like andesite or 
basalt, whereas in a single small restricted group, as in some alkalic 
families, there may be a superabundance of names for closely 
related and essentially identical types. The terms andesite and 
basalt, especially, are greatly overworked, a circumstance that results 
in confusion in several fields of peti rological research, notably that of 
yetrographic provinces. 
Dr. Holmes notes some of the disadvantages of the prevalent 
fashion of basing new rock names upon geographical terms. ‘This 
method certainly brings about some ugly and cacophonous results, 
many petrographers having apparently not considered the question 
of euphony in naming their rocks. It is natural to prefer riebeckite- 
aegirine-eranite to fasitibikite; and all petrographers will 
approve of the condemnation of such monstrosities as /hawavite, 
anabohitsite, and others that could be mentioned. Dr. Holmes seems 
to prefer the alternative method of prefixing a locality name 
to well-known petrographical terms, on the model of M arkle basalt, 
Ponza trachyte, etc.; or using compound mineralogical prefixes 
inthe same way. He states that names such as hornblende-biotite- 
granite are self-explanatory ; but they are only so if the content 
of the rock term itself is well understood. The term granite in 
itself is no more self-explanatory than bandaite or marloesite ; 
