162 VOLCANIC EOCKS OF SOUTH-EASTERN QUEENSLAND 



An andesite similar to the above occurs on the old 

 Warwick coach road on tlie east side of the ]\Iain Range. 



Specimen 7. — Locality: One Tree Hill, near Point 

 Danger. This occurs as a flow about 30 feet thick, capping 

 the Paleozoic schists. Parts of it seem somewhat agglo- 

 meratic, and rounded fragments of finer-grained, almost 

 glas.sy. andesite are seen in it. One frequently finds 

 quartzite and sandstone fragments which have been caught 

 up in the flow. This material is apparently part of the 

 same flow which occurs at Observation Hill or Razorbaek 

 on the New South Wales side of the border. They are 

 only separated by a few hundred yards and are at the 

 same level, have the same thickness and general relation- 

 ships, and are indistinguishable either in the hand-specimen 

 or microscopically. The analysis of the Observation Hill 

 rock may thus be regarded as holding for this rock. In 

 the hand-specimen the rock is a very fine-grained, compact 

 dark material which has occasional phenocrysts through 

 it. Microscopically it shows a hyalopilitic groundmass 

 with occasional phenocrysts of medium andesine, AbgAug, 

 augite and hypersthene. This is the only rock in which 

 hypersthene has been definitely recognised, and it occurs 

 in long crystals reaching 1-5 mm. in length, showing marked 

 pleochroism and having a strong resorption border. The 

 plagioclase phenocrysts which are sub-idiomorphic and 

 range up to 1 mm. in length are remarkable for the 

 numerous regularly arranged inclusions ; in some cases the 

 inclusions seem to form the major portion of the crystal. 

 (See Plate XIII., fig. 6.) In almost all cases there is a 

 narrow outside fringe of felspar clear of inclusions, but 

 as a rule the rest of the crystal contains them, except 

 occasionally the central portion. The arrangement is in 

 many cases zonal but this is not universal. The exact 

 nature of the inclusions is difficult to determine, but in 

 these felspars they seem to be small patches of glassy 

 matrix. The groundmass contains a large amount of brown 

 glass which is not very evenly distributed, and here and 

 there there are small patches free from augite and plagio- 

 clase. The felspar shows lamellar twinning only as a rule, 

 and it is a medium andesine, the laths of which have an> 

 average length of -15 mm. The augite granules are very- 

 fine and distributed evenlv. 



