42 Diorites and Granites of Swift's Greek, 



of the plates and perpendicular to them a more or less wide 

 margin of colourless overlapping fibres. Some alterations 

 have produced aggregates of colourless scales which have a 

 strong resemblance to talcose pseuclo-morphs after horn- 

 blende * such as I have observed elsewhere. Connected with 

 these alterations and throughout the altered spaces patches of 

 iron ore (magnetite) have been deposited either irregularly 

 or between the fibres, and similar deposits have been made 

 in irregular branching cracks which traverse the whole 

 mass. The alterations, as might be expected in such essen- 

 tially magnesian minerals, are rather serpentinous and talcose 

 than chloritic. 



Here and there throughout the mass I have observed what 

 seem to be alterations of some original mineral constituent. 

 They are very finely fibrous, the fibres being strictly parallel 

 to each other. They are faintly yellow and dichroic. 

 Optically the plane of vibration accords with the direction 

 of the fibres. Unless these are allied to chrysotile I am 

 unable to suggest their nature. 



Pyroxene. — This mineral species is very rare, and I have 

 only found it in the massive very hornblendic diorites of the 

 Gum Forest; very rarely in the coarse grained granitic 

 diorites of the lower parts of Riley's Creek, and in the 

 amphibolite dykes. It is invariably almost colourless in 

 the thin slices or only faintly yellow or brownish yellow. 

 It has the character and cleavage of augite. The angles 

 of obscuration in the slices I find to be 30° to 44°; none of 

 the slices are sensibly dichroic. It occurred, without one 

 exception, in more or less imperfect crystals having the 

 form of augite. 



The alteration of this pyroxene has produced an almost 

 colourless chlorite otherwise similar in character to that I 

 have found elsewhere derived from hornblende. It is rather 

 broadly fibrous, wavy, and but faintly dichroic. Iron has 

 been separated either from it or from the associated horn- 

 blende, and deposited either between the chlorite fibres or in 

 separate masses either as magnetite or as ferric oxide, in 

 which case it is often bright red and translucent. I have 

 also observed under favourable circumstances that the 

 chlorite is often formed of minute, thorn-like fibres, which are 

 either arranged approximately parallel or else as slightly 



* These apparently talcose alterations are not affected by hydrochloric 

 acid. 



