126 G. D. OSBORNE. 



twinning and inclusion of scliiller plates, and in common 

 with the felspar it is noticeably fresh. The felspar exhibits 

 pericline twinning very well, and has the composition of 

 basic labradorite. 



(b) Hypersthene Gabbros grading into Norites. — These 

 rocks are very abundant in the suite of inclusions. The 

 component minerals comprise plagioclase 42%, augite (some- 

 times diallagic) 38%, hypersthene 14%, and ilmenite 4%, 

 with decomposition products 2%. 



The structure is gabbroic and the grainsize coarse and 

 even. Some of the felspar plates exceed 3 mm. in diameter. 

 The order of consolidation has been made out as follows: — 

 Iron ore, if primary, early, followed by augite, which was 

 then quickly succeeded by hypersthene. Some of the 

 augite lias been corroded by the still molten felspathic 

 magma, but no corrosion of the rhombic pyroxene is seen, 

 indicating that felspar and hypersthene commenced to 

 crystallise with but little interval between them. 



The felspar U twinned after the albite and pericline laws, 

 the characteristic wedged-shaped segments in the twinning 

 of gabbroid felspars being seen. The reading for extinction 

 angles measured on the trace of the (001) cleavage in sec- 

 tions parallel to (010) is —24°, indicating an average com- 

 position of Ab 2 An 3 . The boundaries between some of the 

 felspar plates are very ragged and produce very irregular 

 intergranular spaces, in which secondary material has 

 developed. Similar material fills many of the cracks which 

 traverse the mineral. This secondary product has a high 

 birefringence and is probably sericite. There is also some 

 chlorite. Augite varies in degree of development and 

 many small grains are included in the felspar. Pleochroism 

 to a very slight degree is noticed, indicating the existence 

 of a little titanic acid in the pyroxene. The maximum 

 extinction measured is Z A c = 44°. Schiller enclosures 



