Biiildmg Stones of Victoria. 18D 



of ferrous carbonate in the stone, the other three oxides makini^ 

 up the balance with magnesia about 8 per cent. In the case 

 of the Dunkeld and Stawell stones, which are of a different type 

 from the others, the composition of dissolved material is more 

 varied, there being a high percentage of magnesia for iho 

 Dunkeld stone and of lime for the Stawell stone. 



For the Bacchus Marsh stone the ferric oxide is low, while 

 the magnesia and lime are high, especially the magnesia, these 

 two oxides being present in carbonates in the stone. 



The Darley material is high in lime and magnesia, and low in 

 alumina. The material dissolved from the Egerton and Green- 

 dale stones is much the same in composition, with the exceptiorx 

 that the Greendale analysis shows a high lime and very ^ow 

 magnesia percentage, whereas in the Egerton material these 

 two oxides are well distributed. 



6. — Microscopical Examination. 



Stawell Stone. 



Examined under the microscope in thin section, this stone is 

 seen to be made up almost entirely of rounded quartz grains, which 

 are very closely packed together, so that there is a minimum 

 amount of cementing material. A great number of the quartz 

 grains contain numerous needles of rutile. while most of them 

 have apatite, zircon, or small liquid inclusions, so that the 

 «and grains are very probably of granitic origin. These quartz 

 grains are of uniform size, and in nearly every case well 

 rounded, showing that they have undergone a good deal of 

 attrition before being cemented together. There are a few 

 subangular, but almost no angular grains. A very occasional 

 crystal of a light brown pleochroic mineral with a high refrac- 

 tive index is seen, and is probably the mineral sphene. The 

 binding material is in parts seen to be secondary silica, while 

 in other parts it is felspathic. Only occasionally do there 

 occur patches of cement of any size, but the cementing to- 

 gether of a number of small quartz grains by secondary silica is 

 veiy common. In the hand specimen numerous patches and 

 bands of what are termed " flints " occur. On sectionino: these 



