53 



Under the microscope this rock is seen to have a coarser 

 grain than the others, and a strongly marked feature is its 

 crystallization schistosity, produced by folia of biotite separ- 

 ated by quartz granules; the biotite is rather greenish and 

 bleached looking, and there is local development of muscovite. 

 There is a sprinkling of iron ore, and little zircons occur in 

 places. Felspar could not be detected. The knots are found 

 to be irregular rounded patches of very fine sericite, resembling 

 very closely in shape and general appearance the andalusite 

 of some of the other knotted schists. At the edges the patches 

 fray out into the ground fabric of the rock, little tongues of 

 sericite dovetailing in with the biotite (pi. ii., fig. 1). 

 Round the knots the schistosity becomes curved, and strings 

 of inclusions, mostly of quartz and iron ore, run through the 

 sericite, usually in curved lines, and continuing the schistosity 

 just as in the andalusite. Where biotite is included it has 

 been altered to chlorite. Iron ore is far more abundant in 

 the sericite areas than elsewhere in the rock. 



In the immediate neighbourhood of the knots there are 

 occasional crystals of chlorite; these are set in all directions, 

 and often contain inclusions of the other minerals as well as of 

 zircon. Muscovite occurs in similar circumstances. 



The distribution of the sericite knots in the rock is quite 

 irregular, as far as could be made out. 



Except that the knots disappear, the rocks maintain their 

 general characters for some distance along the track. No. 4 

 shows a ground fabric a little finer than that of No. 3, but 

 otherwise identical. The rock is slightly porphyroblastic, a 

 few crystals of chlorite cutting across the schistosity and con- 

 taining numerous inclusions. One section cut parallel to the 

 vertical axis shows boundaries sharp parallel to (001) but 

 frayed out at the ends. Basal twinning is shown. The 

 mineral has rather a high refractive index for chlorite, and 

 resembles chloritoid in many characters, but differs from it in 

 being of a very light-green colour, in having maximum 

 absorption parallel to the base, and in beino^ uniaxial 

 (pi. i., fig. 5). 



At the old tunnel, driven into the cliff about 150 to 

 200 yards from the contact, the rock (No. 5) is black and 

 perfectly massive, with very irregular fractare. It is seen 

 under the microscope to be a fine-textured mosaic of quartz 

 and biotite with some plagioclase, and a little apatite and 

 zircon. The rock has been entirely recrystallized, and 

 resembles some of the inclusions in the granite of Granite 

 Island and Port Elliot. There are no traces of lamination 

 or schistosity. 



