12 



perthite, but it must be admitted that the lime is rather high, 





I. 



II. 



III. 



IV. 



SiO^ 



.. 64-54 



■ 65-00 



64-96 



65-05 



Al,03 . 



.. 19-34 



19-50 



18-91 



19*19 



Fe,03 : 



tr. 



-35 



-43 



•28 



MnO . 



tr. 



tr. 



tr. 



tr. 



MgO . 



.. tr. 



•05 







CaO . 



,. 1-24 



•30 



:32 . 



-41 



Na^O .. 



. 2-88 



3-03 



3-31 



3-57 



K,0 .. 



. 11-84 



12-36 



12-09 



11-19 



H3O .. 



-58 



-26 



-18 



•15 



Total 100-42 100-85 100-20 99-84 



Sp.gr. 2-562(9) 2-568 — 2*564 



I. Phenocryst from Port Victor granite. H. W. 



Gartrell, Trans. Roy. Soc. S. Austr., vol. xxvii , 



1903, p. 257. 



II. Perthitic felspar, Westfield, Mass, U.S A. W. H. 

 Warren, Proc. Amer. Acad, of Arts and Sci., vol 

 51, 1915, p. 139. 

 III. and IV. Perthitic felspars, Finland. Anal. Makinen. 

 Quoted by W. H. Warren, loc. cit. 

 as is indicated by comparison of the analyses given above. 

 Some of the lime would be accounted for by the inclusions of 

 apatite and of andesine which are present, but even making 

 allowance for these it is difficult to explain the figures. 



Tlie proportions of the various felspar molecules cal- 

 culated from the analyses for the Victor Harbour and one of 

 the Finland occurrences are: — 





I. 





IV. 



Or 



Ab 



An 



65-7 

 22-91 O..Q 





67-2 

 32-8 



The felspar then is 

 microcline. 



to be regards 



^d 



as a microperthitic 



The phenocrysts contain inclusions of biotite in good 

 crystals up to about 25 mm.; this appears exactly of the 

 same kind as that found elsewhere in the rock, but of smaller 

 size and idiomorphic form. Occasionally the biotite is accom- 

 panied by muscovite either well crystallized or very ragged. 

 Zoned plagioclase crystals up to 2 mm. in length and of the 

 composition of andesine or oligoclase are also included. Quartz 



(9^ A re-dotcrmi nation gave this result. Gartrell's original 

 figure was 2582. 



