J. A. Thomson — Rocks of Western Australia. 



217 



Orthite occurs in the centres of fairly large prisms of epidote, and 

 has determined pleochroic haloes in the biotite. Zircon and apatite 

 are abundant in minute prisms. Of these rocks, the one is well 

 foliated, the other massive, and mineralogically they differ chiefly in 

 the larger amount of hornblende compared to biotite in the latter. 

 The massive rock might easily be taken in the hand-specimen for an 

 ordinary granite, but from its structural peculiarities must be assigned 

 to the gneiss complex, which at Albany is intruded by a coarsely 

 porphyritic pink granite of probably much later age. Among the 

 gneisses garnetiferous varieties were seen, but have not been studied 

 in thin section. 



E^ Apatite. 

 1^ Orthite. 

 WM Zircon. 



Fig. 2. Detail from gneiss showing biotite myrmekitically intergrown with 

 quartz in the bottom left-hand corner and associated with and partially- 

 enclosing orthite, apatite, magnetite, and zircon. Magnification, 34 diam. 



The writer's thanks are due to Messrs. A. Gibb Maitland, Harry P. 

 Woodward, and C. G. Gibson for unfailing kindness during his 

 residence in Western Australia, and for much verbal information 

 which has enabled him to form clear views on the geology of districts 

 which he has not been able to visit. To Dr. J, M. Maclaren, also, 

 he is indebted in a manner difficult to estimate, since most of the 

 above ideas were freely discussed with him during a year's close 

 association. None of these gentlemen, however, can be committed to 

 the classification outlined above. 



