504 



REPORT OF NATIONAL MUSEUM, 1900. 



Drift and its junction with the Hart River. The dr}' diggings are 

 chiefly in Griqualand-West, south of the Vaal River, on the border of 

 the Orange Free State, about 640 miles northeast of Cape Town. There 

 are here a number of limited areas approximate!}' spherical or oval in 

 form, with an average diameter of some 300 yards, the entire produc- 

 tive area being all within a circle having a radius of about 2 miles. 

 These mines were originally worked as individual claims, but they are 

 now all consolidated in one gigantic monopoly which practically con- 

 trols the diamond output of the world. Some idea of the enormous 

 output of the region ma^' be gained from the statement that from 



DIAMOND CRYSTALS. 



Kimberly mines, South Africa. 



Specimen No. 84799, U.S.N.M. 



1867 to 1887 over 33,000,000 carats, or more than 6i tons of diamonds 

 have been taken out, valued in the rough at $225,000,000, and after 

 cutting at $450,000,000. 



At the Kimberl}' mines the diamantiferous area is inclosed in a wall 

 of nearly horizontal l)lack carboniferous shale. The upper portion of 

 the deposit consists of a f ria])le mass of pale yellow color, called the 

 "yellow ground." Below the reach of atmospheric influences the rock 

 is more firm and of a bluish green color; it is called the " blue ground. " 

 This consists essentiallv of a serpentinous breccia inclosing fragments 

 of carbonaceous shale, ])ronzite, diallage, garnet, magnetite, etc. The 



