altered as are all the included rocks. In the centre it is 

 grey-green in colour and closely resembles the breecin lil'in-- 

 the Hornsby neck. It is made up of fragments of shale, 

 sandstone,quartzite, conglomerate, plutonic rock and basalt. 

 Adjacent to the basalt intrusion it is locally hardened into a 

 dense grey or brown and black rock. The microscopic 

 structure of this rock reveals many interesting points. It 

 is composed of quartz grains cemented by a chloritic 

 material, fragments of shale and chert, and also of basalt. 

 The most striking feature of the basalt is its well marked 

 flow structure. Two types occur, the one holocrystalline 

 the other hypocrystalline. The latter is composed of 

 plagioclase laths, (rather decomposed) arranged in a parallel 

 direction and set in a deep brown glass. In this also are 

 idiomorphic olivine crystals changed to iddingsite, forming 

 a single plate placed transversely to the length of the 

 crystal and with strong pleocliroism, the colour changing 

 from pale yellow-brown to deep green. Some more rosette 

 like aggregates of fibres or flakes of similar pleochroism 

 replace other crystals of olivine. These may be iddingsite 

 also. With this a varying amount of carbonate is usually 

 present. 



The holocrystalline type contains parallel laths in a finely 

 granular mass of augite and magnetite. This latter mineral 

 is also aggregated into long bands parallel to the general 

 flow direction. Iddingsite after olivine is also present. 

 These crystals were beautifully idiomorphic and arranged 

 parallel to the flow. 



This rock is carbonated easily. The first sign of this is 

 the production of a white mottling on the grey rock. These 

 white areas are due to the carbonation of the olivine 

 phenocrysts and of the pyroxenes that cluster round them. 

 The magnetites pass into siderite and finally we have 

 plagioclase laths set in a fine carbonate dust. Such a rock 



