BY THE BRITISH ANTARCTIC EXPEDITION, 1907-1909 165 



is abundant in irregular to rounded grains and generally free from inclusions. Sphene 

 and zircon are present, and also a small amount of carbonate. 



P. 376. Pyroxene Granulite, Erratic (Cape Royds). 



Hand-specimen missing. 



Microscopically the fabric is granulitic and the grainsize even, medium. 



The minerals present are : pyroxene, felspar, quartz, sphene, apatite, and sericite. 



Pyroxene is most abundant and forms nearly half the rock. It is, as usual, in 

 colourless allotriomorphic grains. Mostly fresh, but occasionally it has undergone a 

 small amount of decomposition. The felspar is plagioclase twinned after albite, pericline, 

 and occasionally Carlsbad laws. It is in subidiomorphic grains with numerous inclusions : 

 decomposed considerably to sericite, with carbonates present as a side- product of the 

 alteration. Quartz is fairly abundant in allotriomorphic, somewhat rounded grains, 

 comparatively free from inclusions. Sphene is abundant and apatite sparingly present. 



1865. Pyroxene Granulite, Erratic (Cape Royds). 



In hand-specimen a dark-greenish, greasy-looking rock, very much silicified, fine-grained 

 and hard. No foliation visible. Quartz and a ferro-magnesian mineral can be recognised. 

 Under the microscope the fabric is granulitic, and the grainsize even and small. 



The minerals present are : quartz, pyroxene, magnetite, and zircon. 



Quartz is abundant in small rounded grains. It shows shadowy extinctions ; it 

 has very few inclusions. The pyroxene is very light coloured and is in rather rounded 

 grains. Magnetite and sphene are only sparingly present. 



(2) THE SCAPOLITE-BEARING GRANULITES 



This division is practically a subdivision of the acid group. All the rocks in it 

 would, but for the presence of a fair amount of scapolite, belong to group ( 1 ). The amount 

 of scapolite varies considerably in the different members. The mineralogical compo- 

 sition of the various members of the group is very constant, the minerals being almost 

 the same throughout. 



249. Scapolite-bearing Pyroxene Granulite, Erratic (Cape Royds). Hand- 

 specimen missing. 



Under the microscope the rock is granulitic, consisting of small, even-sized, somewhat 

 rounded grains whose average diameter is about T5 mm. Occasional larger grains of 

 scapolite are present, and these are usually so full of inclusions as to present a " sieve " 

 structure. There is not a trace of foliation. The minerals are : pyroxene, scapolite, 

 quartz, felspar, sphene, and magnetite. 



Pyroxene is the most abundant mineral. It is quite fresh and forms nearly half 

 of the rock. It is Diopside. Scapolite is present in subidiomorphic, colourless grains, 

 some of which show two cleavages at right angles to one another. The D.R. is high 

 (•021 approx.) and negative and the mineral is uniaxial. The larger grains contain very 

 numerous small inclusions of a colourless, strongly doubly refracting mineral, which 

 may be sericite. Quartz is fairly abundant in irregular grains, almost free from inclu- 

 sions. Most of the quartz shows an entire absence of strain effects and only a very few 

 show shadowy extinction. The felspar is a plagioclase twinned after the albite law. 

 It is in fairly large allotriomorphic grains. Only a few suitable symmetrical sections 

 are present, and their extinctions point to its being labradorite. It is a good deal 

 dusted with decomposition product and in places is slightly sericitised. Sphene and 

 magnetite are sparingly present. 



584. Scapolite-bearing Pyroxene Granulite, Erratic (Cape Royds). 



The hand-specimen is a dark green mottled rock, very noticeably foliated. Quartz 

 and a clear green pyroxene are easily recognisable. Under the microscope the fabric 

 is granulitic, and the grainsize fairly even and medium. (Plate I, Fig. 3.) 



