354 THE KTMBERLEY GROUP 



tion ; the main shaft has been carried down to a depth 

 of about 2,700 feet, but one of the " prospect shafts " has 

 been continued 300 feet deeper. 



The De Beers Mine is larger than the Kimberley and 

 second to it in richness, but a portion of the " blue- 

 ground " is not rich enough to repay extraction. The 

 workings have reached a depth of 2,400 feet. 



In the early days of this mine there was a dyke of a 

 hard variety of kimberlite traversing the ground in the 

 pipe in a crooked fashion and consequently known as 

 " The Snake," whence the term " snake rock ". Each 

 of these pipes has been proved through the rocks of the 

 Ventersdorp system into the underlying granite. 



The Bultfontein Mine is noteworthy on account of the 

 huge masses of brecciated dolerite in the pipe. Beauti- 

 ful crystals of various zeolites, especially apophyllite, are 

 found in it, usually in the spaces between the blocks of 

 dolerite. 



The Dutoitspan and Wesselton Mines both give a low 

 yield of diamonds. The former mine is the largest of 

 the group. 



The yield of diamonds per 100 loads was in 1908 as 

 follows : Kimberley, 37 carats ; De Beers, 37 ; Bultfon- 

 tein, 32 ; Dutoitspan, 23 ; and Wesselton, 27. 



Though the various outside mines, of which hardly a 

 single one is now (1909) being worked, show many 

 points of geological interest, it is only possible to refer 

 to those of the Newlands l group which are situated in 

 the Harts River Valley. There are four small pipes 



1 R. Beck, Zeitsch. fUrprakt. GeoL, 1898, p. 163. W. Graichen, ibid., 

 1899, p. 417. 



