150 VOLCANIC ROCKS OP SOUTH-EASTERX QUEENSLAND 



rock, with a dull lustre, but showing very evident signs of 

 fluxion. It is made up almost entirely of glass}' material, 

 but it has occasional phenocrysts of sanidine, and possibly 

 anorthoclase. These phenocrysts are rounded and they 

 occur up to 1-0 mm. in diameter. The rock is obviously 

 a more quickly cooled portion of the same material which 

 produced the above rock, as one can see intermediate stages 

 between the two. The groundmass shows strong fluxion 

 structure and it is partly microfelsitic. The glassy portion 

 of the rock is corroded Avith aggregates of microlites which 

 take up a variety of shapes, many of them radiating, but 

 feathery and allied forms are common. Microspherulitic 

 structure occurs here and there. There are no perlitic 

 cracks. Name: Trachy tic Pitch stone. 



Specimen 131. — Locality: Woodhill, portion 122, parish 

 of Logan. This rock is in a very altered condition, and 

 it is a matter of great difficulty to obtain a specimen fresh 

 enough for sectioning. It is found, however, to be holo- 

 crystalline, and to be made up of sanidine, ? oligoclase and 

 chlorite, magnetite and limonite being also abundant. The 

 rock is really too altered to determine exactly, but it is 

 in many respects similar to the Cainbable Creek trachyte, 

 although the presence of the acid plagioclase is rather a 

 variation from that. Name : Trachyte. 



Specintoi 230. — Locality: Portion 136a, parish of Esk. 

 This rock occurs to the west of Esk, and has been referred 

 to by E. 0. Marks. He stated^^ that the trachyte on the 

 summit of the ridge where it occurs is covered with sand- 

 stone, but such does not appear to be the case. The rock 

 is very weathered, and much resembles a brown sandstone 

 in appearance and also in the manner of weathering. It 

 is a matter of great difficulty to obtain fresh samples, but 

 in portion 136a there is a bluff of material which is 

 weathered out into a cavernous structure and the freshest 

 material obtainable was at the base of the blutt. Fluxion 

 structure is shown very clearly in the massive rock. 



This rock is very much like the brown Helidon sand- 

 stone in general appearance and it is slightly porphyritic. 

 The porphyritic crystals are nearlj^ all short, stout lath- 



^'Q'land Govt. Min. Jour., xiii., July, 1912. 



