BY H. C. RICHARDS. 139 



decay in moist positions, Avliich is what we might expect. 

 The lighter the colour the more ready the decay, is the 

 general rule. Rough-dressed stones weather better than 

 smooth-dressed ones owing to the lesser disturbance to 

 the stone in dressing. 



An examination under the microscope shows the stone 

 to be made up of occasional small cr3"stals of quartz, ortho- 

 cJase, and plagioclase, set in a devitrified felspathic ground 

 mass which often shows the peculiar curved outlines of the 

 originallj- glassy particles (see microphotograph 8, plate IX). 



The density and porosity of this material varj- greatly 

 but it might be taken as a general rule that the more dense 

 the stone the smaller its absorption will be and the better 

 its weathering properties. 



The tests on the tuff from the Spring Hill Quarry 

 which was used in the Dry Dock in 1877 show the absorp- 

 tion was 7.2 per cent, and the specific gravity 2.16, which 

 gives a weight of 1351bs. per cubic foot. This absorption 

 is rather high and considerably more than seems advisable. 

 Three tests for absorption bj" the author on representative 

 sjjecimens of green, white and pink colour, gave results 

 of 4.6, 3.9 and 7.7 per cent, respectively ; the white 

 specimen was very much silicified. 



Several important structures have been built of this 

 material in the rough-dressed condition with sandstone 

 used for the facings, and as the tuff has been well selected 

 the use of the stone has been attended with much success. 



The tuff is multi-coloured with a predominant jjink to 

 purple tint so that the lighter-coloured sandstone gives 

 the necessary relief. 



The stone in the Xormal School (1863) was obtained 

 from the Spring Hill quarry-, that in St. Stephen's Cathedral 

 (1874) from Skyrings quarry, near All Hallows Convent, 

 that in St. Paul's Presbj'terian Church (1887) in Leichhardt 

 Street from the Spring Hill and O'Connelltown quarries, 

 and that in St. Johns Cathedral (1909-11) from the 

 OConnelltoAvn quarry. 



The building occupied by the Police Commissioner in 

 George and Elizabeth Streets is regarded as one of the best 



