Sd6 ' Albert V. James : 



'J'lie following are jjroseiit in order of decreasing abundance : — • 

 Andesine, quartz, orthoclase, biotite. chlorite, sericite, niuscovite, 

 apatite, pyrite, magnetite, arsenopyrite, calcite and zircon. The 

 chlorite, sericite, pyrite, calcite, and arsenopyrite are secondary. 



The extinction angles of the carlsbad and the lamellar twins dis- 

 close the fact tliat the plagioclase is basic andesine. Zoned crystals 

 are very abundant, andj" the zones are seen to be more basic as the 

 centre is approached. Certain bands of the zoned felspai's were 

 sericitized before the others, showing that felspars of that 

 Mcomposition were not so stable in the presence of sericitizing agents. 

 Generally sericitization took place from the centre outwards, i.e., 

 from the basic to the acid plagioclases. In tlie sections studied 

 sericite in its turn tends to be kaolinized. 



Simimarif. — The rock from its chemical and mineral composition 

 and its physical properties is a sliglitly altered granotliorite. In 

 the hand it appears fresh, and ^shows no vsign of weathering. 



In the field it undoubtedly appears to be linked to the Gelli- 

 i)raud mass, which has been described bv Dr. F. Stillwell as a'da,ni- 

 ellite (] 1). Both are 500 ft. high, and have the same mineral com- 

 position, and approximately the same chemical coanposition. It 

 differs from the Gellibrand stock in having a slightly higher 

 lime content, and slightly lower silica content. 



Dr. F. Stillwell found that the proportion of jdagioclase to ortho- 

 clase was less than 2:1 in the Gellibrand stock, but the writer by 

 the Rosival method found the proportion distinctly more than 2 :1 

 in the Bulla .stock, which is adjacent to it. Slight differences in 

 mineral and chemical composition are probably local, for the two 

 rocks are similar in all other important characters. 



Granitic Intrusions. — Near Hanging Valley is a granitic dyke 

 20 feet wide, intruding the hornfels. Near the southern edge of 

 the main granitic mass there are several small dykes of microgranite 

 intruding granodiorite, while north of Bulla bridge there is a 

 dyke of aplite and a small one of quartz, both in granodiorite. 



The dyke near Hanging Valley is evidently a tongue from the 

 main mass, but the microgranite, aplite and quartz tongues 

 appear to have been derived from the acid residue of the magma 

 after the outside portion had cooled and hardened. The magma 

 •evidently sloped the palaeozoic sediments so quietly that the dip 

 and the .strike are not only unaltered up to the southern contact, 

 but are continued at the northern junction. Ilie sediments to the 

 west also arc undisturbed. 



