IGNEOUS ROCKS OF TASMANIA, 301 
gabbros of the neighbourhood, but it now appears more 
probable that the pyroxene is secondary, and that associa- 
tion with lime-bearing rocks supplies an explanation of the 
occurrence. Mr. F. J. Ernst, who has been devoting some 
attention to the problem, recently forwarded to me a slide 
prepared from limestone, which forms a 30-foot band in the 
body of the formation, and drew my attention to the green- 
tufted actinolite everywhere present in it. Mr. George A. 
Waller, Assistant Government Geologist of Tasmania, has 
quite recently investigated the occurrence. He informs me 
that a series of parallel metalliferous belts of the rock which 
we have called limurite* runs in calcareous slates and lime- 
stone, conformable with these in strike and dip. His con- 
clusion is that the ore-bodies are replacement deposits in the 
slates and limestones. 
The question of nomenclature remains; but the nomen- 
clature has largely flowed from and been implicated in the 
preceding exposition of classification. It i$ only necessary, 
therefore, to dwell upon first principles and some of their 
applications. 
A perfect system of nomenclature would be such as should 
give expression to the principles upon which the classifica- 
tion is founded. It might be possible to elaborate such a 
system if we were beginning de novo. But we have to take 
things as they are, and we find the field already occupied 
to a large extent with familiar and well-understood terms, 
€.g., granite, gabbro, syenite, diorite, basalt, rhyolite, ande- 
site, trachyte. These names are sanctioned by use, and 
bear well-known meanings. The intrusive rocks, and especi- 
ally the numerous varieties of them which have sprung into 
existence, as it were, since the establishment by Rosenbusch 
of his dyke-division, have given rise to a wonderful crop of 
new terms. The petrologist now-a-days has hard work to 
keep abreast with the ceaseless tide of new names. 
1. A first principle should be to disturb existing nomen- 
clature as little as possible. A faulty name may have won 
so wide an acceptance that its replacement by a more correct 
one may be disadvantageous. 
2. Provisional names may be used, but should be dropped 
when definitive ones become possible. Thus greenstone or 
trap may be applied in the field to rocks which upon the 
application of laboratory methods reveal themselves as 
gabbro, diabase, or even diorite, and this use is justifiable. 
But its discontinuance after a proper determination has 
* One the occurrence of Limurite in Tasmania. W.H.T. and 
W.F. Petterd. Proc. Roy. Soc. Tas., 1897, pp. 1-6. 
