64 Diorites and Granites of Swift's Creek, 



The section is taken nearly north and south, and thus 

 approximately lies at right angles with the strike of the 

 beds. 



a. The gneissic granite or diorite ends here, and a grey 

 coloured, rather rough-textured schist commences, dipping 

 south at 53°. 



b. A band of granitic rock, much decomposed, conform- 

 ing to the dip and strike of the schist, and about ten feet 

 wide. 



c. The grey schists end here. I prepared a thin slice 

 from two samples which represented their average character 

 from a to c. 



The slices were prepared from schists, one of which was 

 quartzose, and the other fine-grained and micaceous. 



The former I found to be composed of grains and aggregates 

 of grains of quartz, whose outlines are irregular. Between 

 them are ragged-edged plates of brown and dull green mica. 

 The paste cementing the quartz grains has been generally 

 converted into an aggregate of minute scales of colourless 

 mica, in which are far larger solitary plates, showing 

 crystalline outlines, and also masses of slightly divergent 

 plates of the same mica. I regard this as being muscovite. 

 It is, however, the magnesia mica that reaches the largest 

 dimensions, and it occasionally constitutes masses separating 

 the quartz aggregates. There are only very faint traces of 

 chlorite in some of the larger aggregates of muscovite mica. 

 Black material occurs in ragged, opaque, and rather minute 

 forms. It is not affected by hydrochloric acid, and is 

 probably graphite. Other minute, black, or dark brown 

 flakes are slightly translucent at their edges, and are there- 

 fore most likely a form of magnesia iron mica. The fine- 

 grained sample showed me that which the general aspect of 

 the schists in the field had suggested was the fact — namely, 

 that they are mainly composed of mica, the quartz grains 

 being few and small. In one sample, the quartz grains and 

 the mica alternate with each other. The material which I 

 have elsewhere spoken of as the " paste " has been wholly 

 converted into mica, the ground mass being colourless, or pale 

 green muscovite, with numerous flakes of brown magnesia 

 mica scattered through it. There are scarcely any traces of 

 chlorite. In this sample I observed the same opaque black 

 substance in considerable amount, which I have spoken of 

 as graphite. 



d. Aplite in more or less irregular bands, conforming to 



