FROM THE MAINLAND OF SOUTH VICTORIA LAND 229 



There are two specimens of the normal dolerite from one of the Ferrar Glacier 

 Moraines. From this locality, also, is a variation of the usual type which, however, 

 has already been noted by Dr. Prior : this is an olivine -bearing variety with violet 

 titaniferous pyroxene. Both the pyroxene and olivine are ophitic. Magnetite is 

 abundant and apatite unusually so. The structure is typical of the diabases but no 

 micropegmatite appears in the slide. 



A dense variolite from the Stranded Moraines, McMurdo Sound, appear to belong 

 to the dolerite series, and may represent the quickly chilled marginal zone as 

 described by Dr. Prior. 



At Dunlop Island, Cape Roberts, Cape Irizar, and the Moraines 20 miles south-east 

 of Mount Larsen other examples of the usual type met with as erratics. 



At Cape Irizar, dolerite erratics are frequent and some diverge from the usual class 

 by containing a residual devitrified or variolitic glass and in some cases by uralitisation 

 of the pyroxene. One of these erratics from Cape Irizar, judged to be an example of 

 the dolerite formation which has suffered chemical metamorphism, is worthy of special 

 mention. The structure is coarse doleritic. It consists of well-zoned labradorite 

 felspars, a little interstitial quartz, deep-coloured biotite, and much uralitic hornblende, 

 observed, in some cases, to be after almost colourless pyroxene ; accessory minerals are 

 frequent apatite rods, and occasional grains of pyrites and magnetite. No micro- 

 pegmatite is observable. 



Dolerite ; Cape Bernacchi 



A hybrid rock, an erratic from Cape Bernacchi, proves to be a variety of the 

 dolerite of unusual character. This is a dark grey fine-crystalline dolerite studded 

 with somewhat oval patches up to a half-inch in diameter of a pink-coloured coarser 

 crystallisation. These pink patches are arranged with their longer axes roughly 

 parallel, and are suggestive of the amygdules common in lavas. 



Microscopic Characters. Most of the pyroxene of the grey dolerite has changed to 

 uralite and chlorite. The plagioclase is much clouded. Iron ores are abundant in 

 grains, partly leucoxenised. 



The pink areas are more coarsely crystalline and differ in constitution from the 

 main body of the rock as follows : The felspars are orthoclase much kaolinised and 

 stained with haematite. Yellow biotite in small flakes is plentiful. Occasional small 

 idiomorphic hornblendes appear of yellowish and greenish tints. Ilmenite partly 

 leucoxenised in grains. Frequent patches of calcite occupying irregular spaces between 

 the orthoclases. The calcite is generally concentrated towards the centres of the 

 patches, and is always so arranged as to indicate its being the latest constituent. 



The pink patches are regularly distributed. The plagioclases of the surrounding 

 dolerite are arranged with their long axes parallel to the boundaries of the patches. 

 The crystal arrangements in the patches sometimes show a marked radial development. 

 Occasionally the peripheral zone of the patches is rich in biotite. These facts indicate 

 that the pink patches are later solidifications than the main bulk of the rock and are 

 really of the nature of pegmatites occupying what apparently were residual spaces. 



The association of this orthoclastic separation with the dolerite recalls the relation 

 of the residual micropegmatite to the normal dolerite. 



A like case is that cited by Dr. Prior * of a dolerite erratic from Granite Harbour. 



These facts lead to the suggestion of magma -splitting on a larger scale, whereby a 

 magma of the type producing the pink granite might be expected to result from the 

 splitting of the parent, more basic magma, in which the dolerites were concerned, 



* Luc. (tit. 139 



