334 Albert V. James: 



the quartz by its cleavage, Avhieh is easily picked out, and by 

 the numerous and characteristic inclusions. A little tourmaline 

 is found in a few sections, but secondary quartz is present in 

 abundance in all. 



Tlie hornfels close to the contact is very much coarser than that 

 some distance away. 



Owing to the quantity of sandstone wliich characterises the palaeo- 

 zoic rocks of this area, a considerable amount of quartzite has been 

 formed, much of it being thermal metamorphic in type; 



It is interesting to note the difference between the action of run- 

 ning water and the weather on these metamorphosed sediments. 

 They appear to be highly resistant to the latter, but readily suc- 

 cumb to the former, owing to the presence of three sets of joint 

 planes, which divide the rocks into variously shaped rliombohedra. 

 The result is that the stream in flood can break out the rhombs 

 and thus deepen its bed, whereas the ordinary atmospheric agents 

 are not so successful. The importance of jointing is shown near 

 Hanging Valley, where a metamorphosed fault rock of the same 

 material as the hornfels around it has more vSucessfuUy resisted 

 destruction by Deep Creek. The fault lock is not jointed, and the 

 normal hornfels is, thus enabling the stream to remove it block by 

 block. 



Gra7iodiorite. 



Six outcrops are mapped, three large and three small, and they 

 roughly form a ring round Bulla, llie boundary of the north- 

 east outcrop is hidden by later detritus, that has gravitated down 

 from the east. The five outcrops to the north stood out as islands 

 in the lava flood, but the most southerly w'as overwhelmed by it. 



Chemical Character. — The material for analysis was obtained 

 from fresh rock that had been " plug and feathered " on the main 

 outcrop southwest of Bulla. 



It was analysed by Mr. ],^\ Watson, and the analysis is given 

 in tlie following table, together with analyses of other similar 

 u'ocks for comparison : — 



