- 476 T. W. E. DAVID, W. F. SMEETH, AND J. A. SCHOFIELD. 
corroded crystals of a rich brown hornblende, which are sur- 
rounded by a ring of magnetite (opacite) dust, which varies in 
amount from a thin layer to a complete absorption of the 
original mineral. (Plate 14, fig. 3.) : 
Olivine-Dolerite, No. 14. 
This rock has suffered considerable alteration. The felspars 
are lath-shaped, not much decomposed, but the broken and 
irregular lamelle give evidence of considerable crushing. These 
felspars have a tendency to aggregate into radial or fan-shaped 
groups which might be considered as a poor attempt at ‘ centric’ 
or ‘ocellar.’ structure. | 
The augite is brown in colour, the depth increasing toward the 
periphery of the grain. It occurs in irregular grains partly 
moulded on the felspars, and giving rise in places to ophitic 
structure. Most of it is fairly fresh, but in places it has been 
converted into a felted mass of chlorite fibres, and possibly also 
serpentine or other ferruginous silicates. 
The olivine is in large grains, frequently with idiomorphi¢ 
contours. These have for the most part been converted into 
serpentine, without separation of magnetite dust, but coloured in 
patches by homogeneous aggregates of chlorite fibres. 
Magnetite crystals are present, together with irregular masses 
of secondary magnetite. Specular hematite seems to be present 
also, the brilliant faces of the crystals being noticeable in reflected 
light ; some of this is possibly micaceous ilmenite. 
Numerous slender needles of apatite traverse all other com 
stituents, and there are needles of what appears to be 
actinolithic mineral also present. 
Olivine Basalt (Nos. 3a, 3). 
Compact, greyish-black with phenocrysts of augite, olivine, 
and plagioclase. Sp. gr. 2-92. 
In section the rock is clear and fresh. The ground-mass fine 
in texture and composed of plagioclase microlites, minute grains 
Ri DLE ee 
