WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 123 
The gravimetric proportion of the original plagioclase in 
the rock was found to decrease, as the basic type became richer 
in pyroscene towards the margin of the mass, from 36.4 per cent, 
to 23.6 per cent., and finally only 11.1 per cent. 
Biotite in greenish pseudomorphs of chlorite is not found 
in this type normally. Only in the section showing the fresh 
quartz vein does a little appear, giving straight extinction. 
The more oxidised variety occurs in small but variable 
quantity. However, large patches of iron-ore have in many 
cases the appearance of pseudomorphs of this mineral and where 
the original character of the mineral is more recognisable it has 
often set free an abnormal quantity of iron-ore — a titaniferous 
magnetite or ilmenite with lamellae intersecting at 60 degrees, 
One crystal appears thus — 
The outlines of the less altered mineral are often irregular. It 
lies in the borders of the augite and in the hornblende and several 
sections measure about .35 mm. by .15 mm. 
Calculating the quantities of pseudomorphs as weU as the 
less altered mineral it was found that the proportion of this 
richly ferriferous biotite showed a gradual increase as the tj^Q 
became more basic from 2.1 per cent, to 8.2 per cent. 
Hornblende occurs in two varieties, one pale green and almost 
colourless in ordinary light, the other giving shades of brown, 
greenish-brown, golden-brown to a deep yellowish ochre. 
Fig 8. 
