NOTES ON ANTARCTIC ROCKS. . 489 
contours, are frequently simply twinned and slightly pleochroic. 
The colour varies from a greenish-brown to a violet-brown in 
different crystals and frequently in the same crystal. Sometimes 
this change of colour takes the form of zoning, the kernels being 
greenish and the outer shell violet, and sometimes the two colours 
seem irregularly intergrown. 
There are also a few corroded remnants of a brown hornblende. 
The original hornblende crystals are in several instances repre- 
sented by remarkable pseudomorphs, similar in many points to 
those described in Basalt No. 5. There are, however, some 
features present in these which render a separate description 
desirable. 
The ground-mass of these pseudomorphs consists @f granules 
of almost colourless augite. These granules have in their 
interstices or intergrown with them little specks of colourless 
isotropic material, numerous elongated and branching parones 
of dark brown to opaque material similar to the fucoid-like in- 
clusions described in No. 5, and finally many prismatic and 
granular pieces of brownish-yellow olivine similar to those in the 
base of the rock. A small piece of the original brown horn- 
blende may or may not remain in the centre. 
The augite framework, which appears to be in irregular granules 
owing to the number of these inclusions in it, is in reality optically 
continuous. In one case it is twinned, one half of the pseudo- 
morph extinguishing at a different angle from the other. As = 
hornblende remains, it cannot be ascertained whether this twin- 
ning occured in the original mineral. Further, it appears from 
‘wo of the pseudomorphs that this secondary augite has its plane 
of symmetry coincident with that of the hornblende. In one of 
these (Plate 13, fig. 5) which appears to be a section parallel to 
010, the hornblende extinguishes at an angle of 16° with 508 
*ertical axis (shown by the prismatic cleavage), while the augite 
extinguishes at 43° on the opposide of the vertical axis. In the 
other case (Plate 13, fig. 6) we have a section approximately - 
right angles to the vertical axis as shown by the shapely defined 
