492 F. Diwey—The Magnesian Group of Igneous Rocks, 
Southern Eyre Peninsula, the theory has been held to be 
inapplicable.* 
VI. RELATION oF THE MAGNESIAN GRouP oF IGNEOUS RocKS TO 
THE ALKALINE, CaLc-ALKALINE, AND OTHER SERIES OF ROCKS. 
A number of petrographic suites and series are already more or 
less well-known, and an attempt will be made in the followmg 
paragraphs to show what relation they bear to the Magnesian 
Group of rocks. 
The series of rocks which most closely approaches the Magnesian 
Group is the Charnockite-Anorthosite Series proposed by 
Rosenbusch ;? this series is said to contain many intermediate 
stages between the acid charnockite and the basic anorthosite, 
and also to possess peridotic and pyroxenic end-members. It 
should be noted, however, that many anorthosite masses contain 
only a small proportion of rocks rich in magnesium. The series is 
much more frequently found in association with the Calc-Alkaline 
Series than with the Alkaline, but it nevertheless differs considerably 
from the Calc-Alkaline Series in chemical composition and in rock 
types. Rosenbusch attempts to compare the chemical characteristics 
of the three series by taking four analyses from each, ranging through 
acid to basic types; the value of this comparison, however, is 
reduced by the fact that so few analyses are chosen while each 
series exhibits so many varieties, and more especially by the fact 
that the four analyses representing any one series are not of rocks 
of any one locality, or even of one continent. It is sufficiently _ 
evident, however, that the three series coincide at their acid and 
basic extremes, shown, for example, in that they all pass with 
decreasing silica into peridotites and pyroxenites. It is interesting 
to note that Rosenbusch has here made the term “ charnockite ” 
of general application, in spite of the fact that Holland emphatically 
declared ° that it ought not to be used outside India; if the term 
had not been so extended, however, a new term would have been 
necessary for general application to those groups of rocks, now 
known in many parts of the world, that closely resemble the 
Charnockite Series of India in all essential respects. Moreover, 
since the term was extended by Holland himself from the rock- 
name Charnockite to the name of the whole series, it is only logical 
to extend it to similar series elsewhere. 
The Magnesian Group embodies the greater part of the 
Charnockite-Anorthosite Series, and includes also the highly 
nagnesian rocks commonly associated with this Series. It is at 
present uncertain, however, where a distinction may be drawn 
1 C. E. Tilley, ‘‘ The Granite Gneisses of Southern Eyre Peninsula (South 
Australia) and their Associated Amphibolites”: Q.J.G.S., vol. Ixxvii, 1921, 
p. 7. 
2 Elemente der Gesteinslehre, 1910, p. 187. 
* “ The Charnockite Series”? : Mem. Geol. Surv. India, vol. xxviii, 1900, p. 131. 
