96 THE BI]S'GEHA DIAMOND FIELD. 



Wash-dirt N'o. 1. 



This is a pale brown clay, binding together Avell-rolled pebbles, 

 subangular and angular fragments of vaiiously coloured jasper, 

 red, green, brown, &c. Also black flinty slate, tourmaline, argil- 

 laceous sandstone, and shale, &c. 



Wash-dirt No. 2. 



This is rather darker in colour than JSTo. 1, and the clay is more 

 tenacious, the contained pebbles are of much the same character; 

 the clay has a brecciated structure, and diff'ers in colour in parts, 

 fragments of it being nearly white. On the spot, when freshly 

 dug out, portions of tlie clay are of a bright green colour, due to 

 the presence of a ferrous silicate, which, by exposure to the air, 

 absorbs oxygen, and passes into the reddish ferric silicate which 

 imparts the red colour to the clay.. 



Wash-dirt No. 3. 



This kind contains a larger proportion of pebbles than either 

 No. 1 or No. 2 ; it is of a light colour, and much less indurated, 

 being of a saudy nature. This also con! aius pebbles of argillaceous 

 shale. 



Unrolled blocks of the bed rock are met with in all the drift. 

 In all three we find occasional minute crystals of selenite, pro- 

 bably of very recent origin. 



During-tlie process of extracting the diamond from the wash- 

 dirt, the material is sized as it passes through the machines ; but 

 as it is hardly necessary to consider these sands and gravels %g])^- 

 rately, it will be as well to consider their constituents merely, 

 irresjiective of the size, since they all contain nearly the same 

 minerals, although not in the same proportions ; but as the large 

 pebbles and boulders which are remo\ed immediately after the 

 stuff is puddled do ditter from the finer j^arts considerably, we 

 sliall take them by themselves. 



Pebbles and Bouldtr.t. 



These consist of masses of red, green, brown, and other coloured 

 jasjiers ; white quai-tz, common agate, blaciv flinty slate ; fine 

 sandstone, into which manganese and iron oxides have infiltered, 

 leaving dendi'itic markings between the joints. Many of the peb- 

 bles arc also coated externally in the same way. Nodules of 

 magnesite and concretions of limonite or brown iron ore, of con- 

 centric structure, — some of the magnesite still showing the limon- 

 ite in situ. Eolled masses of hard compact brecciated conglomerate, 



