WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 
117 
tion. It is in yellowish grains with pleochroism, /3 b^o^\Tlish- 
green, a and y green and pale chrome. Other products are a 
dark-brown sphene and a blood-red haematite. 
Inclusions are abundant, comprising rather large prisms of 
apatite and zircons up to .07 mm. in length, surrounded by 
pleochroic halos. 
The gravimetric proportion of the chlorite pseudomorphs 
after biotite is very variable in the different sections in this series. 
There is another mineral present in variable quantities, 
unidentified " in the Memoir, which occurs in such a fashion 
as to suggest its derivation from a biotite which was originally 
more ferriferous and titaniferous than the biotite now showing 
a merely chloritic alteration. It is rarely present in the most acid 
specimens, but becomes an important constituent in the grano- 
dioritic t}^e. 
I am indebted to Mr. A. Harker, F.R.S., for the suggestion, 
based on my wTitten description, that the mineral is merely a 
biotite which is undergoing a change due to oxidation foUowdng 
•chloritization. 
In some sections it is frequently difi&cult to distinguish this 
mineral from the ordinary biotite. Its outline is sometimes 
hexagonal. The extinction is nearly straight. In longitudinal 
sections its ends are frequentl}^ ragged, and usually show the 
same pseudo " resorption border " as the biotite. Its refractive 
index is high, but apparently less than the chloritized biotite. 
In plain hght it is of a turbid brownish colour and is almost opaque 
between crossed nicols. Its pleochroism is slight, but oblique 
sections show light brown and browrnish-ohve. Under a high 
power the lines of apparently opaque iron -ore are often found to 
be reaUy semi-opaque browTiish particles, almost ultramicro- 
scopic in size. But in other sections they are undoubtedly iron 
ores, mostly leucoxene after ilmenite. 
