41 
No. 464. 
The composition of this rock is as follows :— 
(1) A ground mass consisting of a considerable amount of iron ore, 
apparently magnetite ; (2) very numerous, somewhat stout, hut very 
minute prisms of almost colourless crystals of augite in which the extinction 
angle, c' :r, was as high as 50° 12'. Although faintly flesh-coloured they are 
not sensibly pleochroic ; (3) contemporaneous with this augite are crystals 
of biotite, large in size compared with the augite, and strongly pleochroic in 
shades of dark brown to almost complete absorption of the ray; (4) the 
latest generation is of small, but comparatively stout, lath-shaped felspars, 
in some cases not showing any twin structure. The only extinction 
measurement I could obtain was 9° 39' and 9° 41' on either side of the 
twin plane. 
In the ground mass are scarce phenocrysts of relatively large size. 
They are colourless, showing a well-marked prismatic cleavage, and with an 
obscuration angle in one case of c : c of 34° 5'. The central part is sur¬ 
rounded by the same mineral in which the cleavage is approximately 
perpendicular to the surface of the interior crystal. This appears to be one 
of the iron-free monoclinic pyroxenes. 
This rock may be described as an augite-bearing diorite-porphyrite. 
The above series of holocrystalline igneous rocks consists of several 
slightly different forms of quartz-diorite. 
No. 455. 
This slice is composed of clastic grains of quartz, closely compacted 
together with very little cementing material, which in part is muscovite. 
No. 456. 
This also is a very quartzose rock, consisting of numerous clastic grains 
of quartz set in a mass of still finer quartzose material, the finer cementing 
material being muscovite in small amounts. 
These rocks may be described as quartzites which have undergone 
metamorphism. 
12th March, 1901. 
