44 Diorites and Granites of Swift's Creek, 



or the angle was so small that the disturbance of the cross 

 was barely perceptible. 



One variety of the binaxal magnesia mica I have found 

 to be peculiar to the anorthite diorites of the upper part 

 of Riley's Creek and of the Sheep Station Creek Gap. It is 

 red by transmitted light, and has a peculiar coppery sheen 

 by reflected light. It is strongly dichroic in shades of 

 yellow to dark red and almost black. It is decidedly 

 binaxal. It occurs in slightly divergent groups between 

 the felspars, and also intimately intergrown with horn- 

 blende. (Fig. 23.) 



The inclusions which I have observed in the magnesia 

 mica are almost wholly apatite and magnetite. The former 

 is found to penetrate the various plates, and, in some 

 instances, assuming the form of the mica to be rhombic, to 

 be arranged parallel to the prismatic sides. Very rarely I 

 have observed minute plagioclase prisms, amphibole particles, 

 or portions of ground mass, but such occurrences are very 

 exceptional. 



These micas are extremely well preserved, and only 

 rarely show signs of alteration or decomposition. The 

 alterations produce a substance which I cannot distinguish 

 from the chlorite resulting from the alteration of horn- 

 blende. In places the whole of the mass of mica plates has 

 been altered, while elsewhere the changes have affected only 

 individual plates. 



Figs. 24, 25, are given to illustrate the above statements. 



Titanite. — I have only rarely been able to identify this 

 mineral, even after very careful and special examination of 

 those examples in which it might be expected to be present. 

 Most commonly it is in crystalline grains, associated with 

 hornblende or magnesia mica. 



Apatite is of very common, almost universal, occurrence 

 in the diorites, and, I think, especially in those which are 

 most granitic in character. I have not observed any special 

 features to note. 



Magnetite. — I have already referred frequently to magne- 

 tite, and I may now only add that much of that seen is 

 probably of secondary origin, and due to alteration of 

 amphibole, magnesia mica, and, in a less degree, of pyroxene. 



Pyrite occurs here and there in the more basic diorites,. 

 and especially in the neighbourhood of the mineral veins. 

 In the former cases it is most frequently found in granules, 

 in the latter crystallised in modified forms of the cube. 



