DIAMOND-FIELDS OF SOUTH AFRICA. 881 



Throughout the finest of this heavy sand minute diamonds occur, 

 some so small that they are only recognizable by the aid of a lens. 



As an instance of the yield of diamonds from Kimberley Mine, I 

 may state, on good authority, that two claims, measuring together 

 60 x 30 feet, and worked to a depth of 150 feet, yielded 28,000 carats 

 of diamond, or 2-8 carats per cubic yard of ground. 



The claims on the boundary of the pipe at Kimberley are worked 

 at a depth of 200 feet from the surface ; those in the centre have 

 been mined with less spirit, as they are considered less productive. 

 The water met with, though comparatively insignificant, costs a 

 large sum to get rid of, in consequence of the inefficient machinery 

 employed and the absence of system in draining the mine ; it is now 

 utilized at the surface by washing-machines. Another heavy expense 

 in working is caused by the ever- increasing liability of the unsup- 

 ported sides to fall into and bury the claims. 



" Trap Conglomerate" is mentioned in my former paper ; and that 

 occurring near Pniel is classed with the rock thus named by Wylie, 

 which occurs along the edge of the Karoo Beds. Microscopic exami- 

 nation proves them to be quite distinct ; and the manner of occur- 

 rence of the latter in Natal* shows it to be of sedimentary origin, 

 while that mentioned as existing at Pniel is certainly intrusive, and 

 of more recent date than some of the amygdaloids. 



II. Gold. 



Gold is mined for at Lydenburg and Eersteling, ia the Transvaal 

 Republic. 



Lydenburg Gold-field is situate in a mountainous tract of country 

 (lat. 2d° S., long. 31° E.), the highest paaks of which rise fully 

 7000 feet above sea-level. The geological disposition of the rocks 

 gives a peculiar character to the physical geography of this dkirict. 

 The rocks strike about N. and S., and dip at an angle of about 

 15° to the W. ; in consequence the E. sides of the mountains are 

 abrupt, while on the W. the slopes are gentle (see fig. 1). 



This region, and a considerable portion of the Transvaal Republic, 

 are occupied by beds of sandstone, mudstone (sometimes thinly 

 laminated), white and red quartz rock, cherty and crystalline lime- 

 stones (the cherty limestone thickly seamed with small veins of chert 

 and quartz lying in the planes of bedding), thin beds of black calca- 

 reous sandstone, quartz-breccia (a rock resembling quartz rock that 

 has been shattered and the cracks filled with vein-quartz &c). Inter- 

 calated sheets of diorite are numerous; and dykes of the same occa- 

 sionally intersect the stratified rocks. Massive diorite occurs about 

 forty miles to the west of Lydenburg ; and probably from it the sheets 

 lying between the stratified rocks have been supplied. 



Quartz reefs occur throughout the area occupied by the above 

 rocks ; they are generally barren-looking, and vary much in strike. 



Diorite on the "VV., and gneiss on the E., appear to be the under- 

 lying rocks of this formation. The age of this series is uuknown, 



* Quart. Journ. Geol. Soc. vol. xxvi. p. 516. 



