l^Y W. H. BRYAN, B.SC. 153 



brecciatioii and grinding-up of the schist, and examples 

 <>an be seen at a number of points outside the periphery 

 of this ntrusion. The breccia is made up of angular 

 fragments o schist of various sizes, but seldom exceeding 

 one inch in length, set in a finely-powdered ground mass. 

 Thi-; rock, as the granite is approached, gradually shades 

 off into a hornfels showing traces of the agglomeritic 

 structure, which in turn is succeeded by a more normal 

 hornfels. 



The mineralogical and textural changes induced in 

 the schists not only vary in the different areas considered, 

 but vary at different contacts of the same intrusive mass. 

 In general, as the granite is approached, the quartz veins, 

 which form a noticeable feature even in the normal schist, 

 become more frequent, until in close proximity to the 

 granite, the whole rock seems to have been silicified and 

 hardened. A marked textural change is to be seen near 

 the Enoggera Reservoir where the heat resulting from 

 the intrusion has converted the normal micaceous schist — 

 already somewhat siliceous — into a hard black hornfels. 

 On the north-north-west edge of the main granite area, 

 and twenty-five yards outside the actual contact, on the 

 Cedar Creek Road, there is a band of rock about two feet 

 in thickness, showing the typical schistose and contorted 

 structure of the Brisbane schists, but made up almost 

 entirely of tourmaline and felspar arranged in definite bands . 

 The tourmaline — which is the black variety schorl — is 

 present as numerous minute acicular crystals all arranged 

 with their long axes parallel to the planes of schistosity, 

 and seems to have taken the place of the micaceous part 

 of the schist ; while the felspar seems to occupy the spaces 

 pre\aously occupied by the small veins of quartz. The 

 whole schist has been so beautifully replaced that the new 

 rock under the closest scrutiny shows every characteristic 

 of the normal schistose structure. Nearer the granite, 

 and almost right on the contact itself, is a larger body of 

 schorl rock composed entirely of tourmaline in the same 

 slender crj'^stals, but in which the oi'iginal schistosity is onlj^ 

 faintly recognisable. This rock contains cavities which 

 are partly filled with well-shaped quartz crystals with 



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