—— 74 
191 
Microscopic Characters.—The rock is essentially a medium 
grained hypidiomorphic granular mixture of quartz and 
albite, with a considerable quantity of chloritic substance de- 
rived from limotite and ilmenite. All the minerals show 
strong evidence of erashing, which has probably materialiy 
modified the original character of the rock. Foliation 
obvious in hand specimen is not distinct under the micro- 
scope. The quartz and felspar call for very little description, as 
they present features similar to those in the three last rocks 
described. In this instance, however, there is more inter- 
stitial quartz and less included in the felspar, which is in much 
smaller pieces. Both minerals are much shattered, and give 
markedly undulose extinctions. In the felspar twinning 
after the albite law is moderately developed, but is very often 
hazy, perhaps owing to strain. Certainly the lamelle are 
often bent and broken. 
The chloritic material is dirty green in colour and is of 
markedly micaceous habit, the plates often being arranged 
in rosettes, which give a black cross between crossed nicols. 
The pleochroism is marked: light yellow when the vibrations 
are perpendicular to the cleavage, greenish when they are 
parallel to it. Double refraction is very weak, the colours 
being the characteristic azure tints of chlorite. Sections 
parallel to the cleavage are sensibly isotropic. The figure in 
convergent light is exceedingly hazy, but appears to indi- 
cate a biaxial mineral. At the edges of each flake the 
colour changes to bright orange-yellow, indicating a more fer- 
riferoüs variety, and there is a corresponding increase in 
double refraction, the colours at the edge being of the same 
order as those of quartz. The original biotite must have 
been strongly titaniferous, as the chlorite which has been 
produced by its alteration is much mixed with granules, of 
greyish sphene, even where no ilmenite can be detected. 
Ilmenite is moderately plentiful in rather irregular grains, 
which in some cases appear to be aggregates of minute gran- 
ules. A certain amount of decomposition into leucoxene is 
noticeable. 
Rutile in small, stumpy pyramids and rounded forms is 
scattered through all the minerals indiscriminately; in the 
chlorite they give rise to dark pleochroic halos. The smaller 
individuals are practically opaque, the larger ones show a 
dark reddish-orange colour by transmitted light. A few zir- 
cons, some of them of relatively very large size, are present, 
and are distinguished from rutile by their lack of colour and 
weaker double refraction. 
