WHITE : OATLAND COMPLEX OF IGNEOUS ROCKS. 131 
The order of crystallisation of the minerals was the same 
in both shdes, viz. : — 
1. Apatite and iron ores. 
2. Augite. 
3. Felspar. 
4. Biotite. 
5. Hornblende. 
6. Quartz. 
The gravimetric mineralogical composition of the two 
sections proved to be 
1. 
2. 
Quartz 
10.03 
10.09 
Felspar 
37.95 
39.49 
Augite 
29.99 
32.57 
Hornblende 
14.70 
12.34 
Biotite 
4.53 
2.88 
Iron Ores . . 
2.80 
2.63 
SUGGESTED HISTORY OF THE INTRUSION. 
Following the great E. and W. earth pressure, which caused 
the complex folding in the island, came the intrusion of an igneous 
rock magma, probably already highly differentiated, as a sill of 
basic rock. 
Afterwards, and the petrological evidence on the whole 
points to the lapse of a considerable period, came a second intrusion 
from the same magma reservoir, probably lace oli tic in habit, 
which lifted the overlying rocks and hy intimate mixture with 
the already consolidated basic rock formed at the plane of junction 
a hybrid or " mixture " rock while the acid magma penetrated 
the surrounding crust of basic rock in innumerable tongues, veins 
and Fasern. 
The last effort of the igneous intrusion to reach the surface 
resulted in the injection of the remaining super-heated siHca-magma 
as a quartz dyke (similar to those at Foxdale, described by Lomas) 
which dissolved some of the last crystallised and fibrous amphibole 
and altered the basic rock at its conterminous parts into a fresh - 
looking augite-diorite. 
