38 



change to bastite is in process, very visible by polarised 

 light. The crystals of augite are much fewer in number, and 

 are mostly somewhat octagonal in section. 



The felspar of the ground mass comprise striped and 

 simple laths, and often show fluxion phenomena. The small 

 extinction angle of the twinned felspars points to oligoclase, 

 and the straight extinctions of the simple laths to orthoclase. 

 There is a quantity of granular quartz in the ground mass, 

 but it is doubtful whether all of it is primary. If it is, it is 

 rather an exceptional occurrence in enstatite-porphyrite. The 

 rest of the ground mass consists of diffused chloritic matter 

 and brown granular aj>parently micro-felsitic substance. 

 Large amygdaloidal cavities are occupied by quartz, epidote, 

 and calcite. Here and there in the ground mass, especially 

 in the neigbourhood of the amygdaloids there are aggre- 

 gations of granular magnetite, obscuring the felspar micro- 

 liths, but little or none elsewhere. The rock evidently 

 belongs to the intermediate division, and is essentially 

 andesitic. 



EXPLANATION OF PLATE. 



Fig. 1. Harzburgite. x 13. Crossed Nicols. The larger crystals are 

 enstatite. Most of the smaller ones are olivine. 



Fig. 2. Olivine Norite. x 13. Crossed Nicols. Shows poly synthetically 

 twinned felspars and meshed olivine. The dark parts are 

 principally enstatite. 



Fig. 3. Pyroxenite. x 18. Crossed Nicols. The field is occupied by 

 part of large diallage crystals, separated by a brecciated vein 

 of small crystals of monoclinic pyroxene, the " mortar structure " 

 of petrography. 



.Fig. .4. Lherzolite. x 13. Crossed Nicols. Shows the granular 

 association of olivine and pyroxenes. This is No. 5 in the paper. 



