BY H. C. RICHARDS. 113 



The stones work freely and although more expensive 

 to dress than the sandstones at present nsed they would be 

 much cheaper to work than the Enoggera or Grejunare 

 granites. Provided fresh and unweathered material is used 

 there is no doubt as to the lasting qualities of the stone. 

 Either rock-faced or smooth-dressed it would look Avell, 

 but in the rock-faced condition it wovdd be very good and 

 easilj' worked. It is difficult to say whether large stones 

 could be quarried, as the jointing is not regular as a rule and 

 is rather more frequent than usual with igneous rocks. 

 Small stones, rock-faced and used as the Brisbane Tuff 

 has been used in St. John's Cathedral, Brisbane, and else- 

 where, would undoubtedly have a \ery handsome effect ; 

 the same stone smooth-dressed could be used for the facings. 

 The quantity of stone is unlimited, and quarrying 

 operations on a large scale could be carried on Avithout 

 detriment to the peaks. 



These stones need earnest consideration and will 

 probably be much used in the future. The cost of quarry- 

 ing and working will be grea^ter than that of the sandstones 

 used at present, such as the Helidon sandstone, but the 

 lasting qualities are infiniteh^ better. 



The specific gra\ity of the stones ranges from 2.47 to 

 2.71 which gi\'es a variation of from 154 to 1691bs. per cubic 

 foot. The stones are practicalh^ non-porous and will with- 

 stand a high crushing strain. 



Rhyolite from Glen Bock, Esk. 

 At Glen Rock, Esk, there is an immense mass of a light 

 yellow-brown rhyolite. The Esk Council has a quarry in 

 this material from which it obtains road metal. The stone 

 is very fine in grain, being only 0.75 mm.* and the arrange- 

 ment of the crystals shows a poor fluxion structure. The 

 minerals present are quartz, and the felspars, anorthoclase 

 and sanidine (see microphotograph 9, plate IX). This 

 rhyolite works very freely indeed for an igneous rock, 

 dresses well, and Avould take a very sharp arris. The 

 rock is rather frequently jointed where it is being 

 quarried at present but no doubt a quarry site for obtain- 

 ing reasonably large stones could be obtained. 



* Richards, H. C. Proc. Rov. Soc. Q'ld., xwii (2). 1916, p. 139. 

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