112 BUILDING STONES OF QUEENSLAND. 



Harcouti Granite. — This grey granite in the form of 

 polished columns is seen in front of .ShaAv & Sons" building 

 (1904) in Queen Street, Brisbaaie. It has also been used to 

 a very limited extent in the base and foundations of St. 

 John's Anglican Cathedral.* 



■ RHYOLITES "' AND " TRACHYTES." 



Glass House Mountains. — South-eastern Queensland 

 is noted the world over for its development of alkaline 

 rhyolites and trachytes. The development at the Glass 

 House Mountains is particularly well-known owing to the 

 peculiar occurrence of these isolated peaks. 



More than one \ATiter has drawn attentioji to the possible 

 utilisation of these rocks for structural purposes, but no 

 attempt has yet been made to Avork the stones. Each of 

 the eight or nine peaks yields a different rock and remarkable 

 variation in appearance is exhibited in each of the particular 

 occurrences. For a full description of the various rocks 

 the reader is referred to the writings of Dr. H. I. Jensen! 

 and of the authorf. 



All the rocks are fine-grained volcanic rocks of a light 

 grey colour ; sometimes the colour is a distinct bluish-grey. 

 The rocks may be regarded as being made up essentially 

 of sanidine (a clear variety of orthoclase) felspar, and of 

 soda-rich augite : quartz occurs in several of the varieties 

 (see microphotographs 10, 11, plate IX). The occurrence 

 throughout the rocks of dark blue and dark green ferro- 

 magnesian minerals often results in a \ery pretty effect 

 owing to their disposition. The dark minerals may be 

 evenly distributed and exist as small specks with a resultant 

 "pepper and salt" appearance. They ma}^ occur as rods 

 and as the rocks typically show fluxion structure the rods 

 are arranged with the longest axes parallel and equidistant 

 apart. On other occasions the dark minerals are arranged 

 in moss-like aggregates. The stone is in close proximity 

 to the railway line between Beerburrum and Glass House 

 Mountains, a little over 40 miles from Brisbane. 



* Richards, H. C. Proc. Roy. Soc. Q'ld., xxiii (2), 1911, p. 204. 

 t Proc. Linn. Soc. :N.P.W., xxxi-xxxiv., 1906-1909. 

 t J'roc. Roy. Soc. Q'ld., xxvii (2), 1910, p. 40.1 



