490 A. LIVERSIDGE 01T THE BINGERA 



greenish siliceous base, and dykes and ejections of intrusive green- 

 stone. The rocks are generally devoid of mica. 



The older Pliocene diamantiferous drift is generally coarse and 

 loose, but in parts cemented together by a white siliceous cement, 

 sometimes green by admixture with silicate of iron; sometimes 

 oxides of iron and manganese are the agglutinating agents. Dia- 

 monds were found in this solid portion. 



The drift consists chiefly of boulders and pebbles of quartz, jas- 

 per, agate, quartzite, flint, slate, shale, and sandstone, with coarse 

 sand and clay. The quartz -pebbles are often incrusted with oxide 

 of iron or manganese. Many of the boulders and pebbles show a 

 peculiar brilliant polish or glaze, not due to friction, since the cavi- 

 ties are equally well polished. Silicified wood is common ; and coal 

 has been found in the river higher up— also Carboniferous fossils, 

 such as Favosites goilandica, and Orthis. 



The minerals associated with the diamond are : — 1, black vesicular 

 pleonast ; 2, topaz ; 3, quartz ; 4, corundum ; 5, zircon ; 6, tourma- 

 line ; 7, black titaniferous iron-sand ; 8, black magnetic iron-sand ; 

 9, brookite; 10, wood-tin; 11, garnet; 12, iron," from tools; 13, 

 gold. 



The diamonds are distributed sparingly and irregularly through 

 the older Pliocene drift. The average weight of the diamonds 

 was 0-23 carat or nearly 1 carat grain. The largest discovered was 

 a colourless octahedron of 5J carats. Average sp. gr. 3*44. 



The newer Pliocene drift also furnishes a few diamonds ; and, being 

 chiefly derived from the older drift, it contains the same minerals ; 

 but a few grains of osmiridium are also found in it. 



A few diamonds have also been found in Victoria. 



The Bingera Diamond-field. 



The workings are about seven or eight miles south of Bingera, and 

 are situated in a basin-shaped valley among the mountains of the 

 Drummond range. This valley is about four miles long, and three 

 miles broad, and opens to the south. The surrounding district is 

 of Carboniferous or Devonian age. The valley seems to have been 

 covered by diamantiferous drift ; but much of this has been removed 

 by denudation, leaving patches. Eunning into the basin are spurs 

 of basalt, which also probably overlies the drift. 



The bed-rock under the drift is an argillaceous shale. Blocks 

 of this are scattered through the lower part of the drift ; and small 

 outcrops of it are seen in one or two places. In some parts there 

 are outcrops of a siliceous conglomerate composed of subangular 

 pebbles with ferruginous cement, sometimes replaced by manganese ; 

 and the junction of the conglomerate with the shale is shown by a 

 small gully. The rocks are much contorted and almost vertical. 

 Diamonds occur in the surface soil over the conglomerate here, but 

 not over the shale. 



All the workings for diamonds are confined to the surface, the 

 drift not being removed to a greater depth than 2 or 3 feet. The 



