Building Stones of Victoria. 193 



the silica occur in the small amount of cementing material in 

 the stone. The iron oxides, magnesia, lime and alkalies are pre- 

 sent to only a slight extent, while carbonates are altogether 

 absent. 



The Dunkeld is a little lower in silica than the Stawell 

 etone, but it contains more combined water and alumina, owing 

 to its larger percentage of cementing material, the alkalies are 

 a little higher, but not present to any appreciable extent, while 

 the iron oxides and alkaline earths are very low. 



In neither of these stones does there appear to be any con- 

 stituent easily affected chemically, under ordinary weathering 

 conditions. 



The Bai-rabool Hills and AjJoUo Bay Stones, from their 

 chemical analyses alone, are seen to be different types of stones 

 from the others, and a very close resemblance exists between 

 the chemical constitution of these two, also a comparison of 

 their analyses with those of the Victorian Dacites shows marked 

 similarities. The silica is low, while the alumina, combined 

 water, and alkalies are high. 



The ferrous oxide in the Apollo Bay stone is about twace 

 that of the Barrabool Hills stone, also the former has a lower 

 ferric oxide value than the latter. It is the relative amount 

 of these two iron oxides which governs the colour of the stone, 

 the more ferrous oxide the greyer the stone, the brown colour 

 of the Barrabool Hills stone being due to the ferric nature 

 of the iron it contains. 



A small portion of the fresh grey Barrabool Hills stone was 

 analysed for ferrous iron, and gave 3.70 per cent., while an 

 adjoining piece of brown stone gave only 1.80 per cent. The 

 presence of the ferrous oxide in the stone must be regarded as 

 a defect, as it is so readily oxidised on weathering. 



lite Bacchus Marsh Stonp. is only moderately high in silica 

 for a sandstone, while the combined w^ater and alumina are 

 high, but this is a natural result of the large amount of argil- 

 laceous material the stone contains. The .ferric iron value is 

 high, and accounts for the brown colour of the stone, Avhile the 

 alkalies occur in the small amount of felspathic material the 

 stone contains. Carbon dioxide occurs to the extent of .32 per 

 cent., and is combined partly with the lime and partly with the 



