US VOLCANIC ABEA OF EAST MOEETO'N, ETC., DISTRICTS, Q., 



i. The rock is of a pale }^ellowish colour, and with a pocket 

 lens one can easily see that it consists of quartz and orthoclase 

 graphically intergrown. The graphic granites which I have met 

 with in the district occur as dykes in the main granite masses 

 and in the metamorphic rocks. They consist of the mother 

 liquor which has been squeezed into cracks in the superjacent 

 granites and sedimentary rocks in the final phases of consolida- 

 tion of the granite mass. 



ii. Under the microscope the rock is seen to consist of a beauti- 

 ful graphic intergrowth of quartz and felspar. A few minute 

 needles of apatite are included in these minerals. 



The felspar is orthoclase and a microperthitic intergrowth of 

 orthoclase and albite. It consolidated simultaneous])' with the 

 quartz. On account of field occurrence this rock is best named 

 Graphic Granite-Aplite. 



Aplite. Loc: Base of Round Mountain, Caboolture- Woodford 

 Road. 



i. The handspecimen is yellowish and resembles metamorphic 

 sandstone. With a lens quartz and felspar are easily identified. 

 The Round Mountain is surrounded by Trias-Jura sandstones 

 on all sides, but at the very base on the south side occurs a small 

 outcrop of this rock which seems to be the summit of an outlier 

 of the Pre-Triassic rocks. 



ii. Microscopic examination. — (1) Texture (a) noncrystalline, 

 (b) medium-grained and even, (c) allotriomorphic granular. 



(2) Constituents (in order of decreasing amount) — (a)plagioclase, 

 (b) quartz, (c) orthoclase. 



(3) The plagioclase forms about 85 °/ of the total felspar and 

 was found to be all albite. The orthoclase forms 15 % of the 

 total felspar. Felspar forms about 64 % by weight of the rock. 

 The quartz forms the remaining 36 % of the bulk. These three 

 minerals are allotriomorphic, and the spaces between the grains 

 are often filled with a micropegmatitic intergrowth of them. 



(4) Some of the quartz consolidated before the felspar com- 

 menced. This shows that the magma must have been very dry 

 and supersaturated with silica. 



