BY THE BRITISH ANTARCTIC EXPEDITION, 1907-1909 167 



sition Ab 1 An 1 . It is fairly fresh and in places has numerous inclusions. Quartz is 

 abundant in rounded, allotriomorphic grains. It shows shadowy extinction but is 

 not granulated to any extent. Scapolite is fairly abundant in allotriomorphic to subidio- 

 morphic grains, which are sometimes ragged. It is pretty free from inclusions and in 

 one or two places exhibits what seem to be traces of albite twinning. Sphene is fairly 

 abundant and zircon is also present, There are a few grains of a light-coloured mineral 

 which is probably diallage. 



(3) THE BASIC PYROXENE GRANULITES 



In this class quartz is either absent or only present in comparatively small amount. 

 The most basic ones approach fairly closely to a pyroxenite. They contain pyroxene, 

 felspar, sphene, quartz, apatite, and magnetite, the pyroxene is the same as in the 

 acid class. The felspar is uniformly labradorite, of composition AbjAn, or very slightly 

 more basic. Sphene is present throughout and is occasionally very large. 



1267. Pyroxene Granulite, Erratic (Cape Royds). 



The hand-specimen is a mixture of light and dark parts ; the light parts are mostly 

 quartz veins and the darker ones are made up of felspar and pyroxene. It is fine to 

 medium grained and shows very little foliation. 



Under the microscope the fabric is hypidiomorphic granular, and the grainsize 

 uneven. Felspar and pyroxene, the two most important minerals, have a tendency to 

 cluster in bunches, each mineral separately. 



The minerals are : felspar, pyroxene, sphene, and apatite. 



The felspar is all plagioclase ; it occurs in subidiomorphic grains very variable in 

 size — some of the grains are as large as 1'5 mm. by 1 nun., while in other places there 

 is an aggregate of very small felspar grains, which may be due to granulation of larger 

 felspar grains. It is twinned after the albite and pericline laws, and symmetrical sections 

 indicate that it is a labradorite with a composition AbiArij. There is very little decom- 

 position, only a few grains being slightly dusted with decomposition product. A little 

 sericite is present and may be from the alteration of some of the felspar. The pyroxene 

 is present as large grains, frequently twiimed. It is very light coloured and has uniformly 

 high extinction angles in longitudinal sections. It is probably diopside but may possibly 

 be referred to malacolite. Sphene is not abundant but is present in unusually large 

 sections, reaching such dimensions as 1*5 mm. by '75 mm. Apatite is also present. 



1515. Pyroxene Granulite, Erratic (Cape Royds). 



Hand-specimen very similar to 1267. 



Under the microscope the fabric is pan allotriomorphic granular ; poikilitic in places by 

 means of the pyroxene and occasionally by the felspar. A considerable amount of foliation 

 is shown by the arrangement in bands of the felspar and pyroxene. (Plate I, Fig. 5.) 



The minerals are : pyroxene, felspar, quartz, and sphene. The pyroxene is very 

 abundant in allotriomorphic grains and forms more than half of the rock. It is colourless 

 and ophitically encloses felspar. Felspar is subordinate in amount to the pyroxene 

 and forms about one-third of the rock. It is twinned after the albite and pericline laws ; 

 the striations are very fine and give a general appearance of rather coarse microcline. 

 It poikilitically encloses quartz and more rarely pyroxene. It has the composition 

 about AbxAn!, obtained by means of symmetrical sections. 



Quartz and sphene are sparingly present. 



e26. Pyroxene Granulite, Erratic (Cape Royds). 



In hand-specimen this is a light-greenish rock, very hard and silicified. Quartz and 

 pyroxene can be recognised. 



Under the microscope this rock varies a good deal in different parts. The section 

 examined shows quite a contrast between two halves. One-half of the section is a 



