VOLCANIC NECK AT THE BASIN, NEPEAN RIVEK. 125 



say. There are however textural changes which are cer- 

 tainly due to the proximity of inclusions. One phase of 

 the basalt consists of small well formed prisms of purple 

 augite which exhibit characteristic transverse cracking 

 and occasional simple-twinning. A little lath-shaped 

 plagioclase felspar (Abi Aiu ), with albite twinning, and 

 subordinate ilmenite complete the mineral constitution. 

 In appearance this rock resembles the so-called "aphanitic 

 dolerites" of Antarctica. 1 



A more normal phase of the basalt consists essentially 

 of laths of basic labradorite, crystals of green augite and 

 iron ore with a little interstitial glass. A few grains of 

 olivine are also present. This olivine belongs to the rock 

 proper, but other extraneous olivine crystals are seen in 

 the slide. These latter are altered and invariably possess 

 a tiny border of diopside crystals. 



The arrangement of the constituents of the basalt gives 

 rise to a pseudo-variolitic texture. The rock probably 

 cooled rapidly. 



4. Inclusions in Dyke No. 1. — This section of the petro- 

 logy has been studied in most detail and it is proposed to 

 consider the rocks in types, the general description of each 

 type being based on the examination of a number of 

 examples. The rocks will be treated in the following order: 

 Gabbros, Hypersthene Gabbros (Norites), Troctolites, 

 Harzburgites, Lherzolites, Dunites, Pyroxenites and other 

 miscellaneous types. 



(a) Gabbros. — True gabbros have rarely been met with 

 at the Basin. Most of the gabbroic rocks are hypersthene- 

 bearing, thus being noritic in character. However, one 

 gabbro has been examined, the component minerals being 

 felspar, augite, magnetite and apatite. The augite shows 



1 W. N. Benson, British Antarctic Expedition 1907-9, Geol. n, p. 153. 



