IHK IMH.KRITES OF KING GEORGE LAND AND ADELIE LAND BROWNE. 255 



the earlier being in thick tabular crystals, up to 3 mm. in length, and zoned (Ab gfi An 75 

 to Ab tt An M ). Schiller inclusions are arranged along the pinacoidal cleavage-planes 

 The later plagioclase laths, averaging "> nun., have a composition about Ab^ An^ 

 (Plato XXXIX Ki.n. 2). 



The pyroxene is all monoclinic, pale-grey to pale purplish-grey, and is, in part 

 at least, enstatite-augite ; it is ophitic towards the felspar. Olivine is represented 

 by abundant small individuals pseudomorphed by brown iddingsite (?), but a few aggre- 

 gates are found representing original olivine nodules now changed to a pale-green strongly 

 birefringent substance, suggestive of talc, and sometimes accompanied by carbonates. 

 The marginal passage of this into a brown-coloured substance suggests that the material 

 doubtfully referred to above as iddingsite may really result from the staining of this 

 green talc-like mineral by iron (Plate XXXIX, Fig. 1). 



The iron ore is skeletal ilmenite with a little magnetite ; it is usually moulded 

 in felspar but enclosed in pyroxene. A little pyrites has made its way along cracks in the 

 felspar. 



There is a small proportion of rnesostasis in the rock, consisting of a greyish 

 mineral that appears to be orthoclase, sometimes in parallel intergrowth with what is 

 probably another felspar, and often crowded with magnetite granules and tiny apatite (?) 

 needles. Very occasionally quartz fills the little interstices between the felspar laths. 



The association of olivine and quartz in the same rock, though not unknown, is 

 rather exceptional. Certainly the olivine is now completely altered, but the identity 

 of the original mineral is beyond doubt. The quartz for the most part has the appearance 

 of being primary, acting as an interstitial filling in which are embedded apatite needles 

 and the ends of plagioclase prisms. A possible explanation is that the olivine grains 

 and nodules represent early intratelluric crystallizations from the dolerite magma, which 

 had sunk to the bottom of the magma-reservoir and were caught up in the still liquid 

 portion of the magma at the time of its injection. 



Specimen No. 456 is a medium-grained rock in which felspar (Ab 35 An 63 ) and 

 >xene are present in about equal proportions, and ilmenite of semi-skeletal habit is 

 unusually abundant. The pyroxene is, in part at least, enstatite-augite, showing the 

 salite striation at times and altering into chlorite enclosing tiny sphene granules, and 

 into brownish uralite, the felspar showing sericitic and calcitic alteration. For the most 

 put the pyroxene is moulded on the felspar, but occasionally the reverse relation holds. 

 rtz occurs interstitially in very small amount and never in pegrnatitic intergrowth, 

 and a very little apatite and biotite are also noticed. A feature of the rock is the presence 

 of irregular interstitial patches of finer grain than the main body of the rock, consisting, 

 ir as can be made out, largely of plagioclase. with subordinate augite largely altered 

 1 - 1 uralite. Ilmenite and magnetite are fairly plentiful in close association with augite ; 

 also elongated, tiny needles of what appear to be apatite, often with parallel arrange- 

 Little flakes of biotite are not uncommon, and there is a mesostasis consisting 



