CATALOGUE OF GEMS AND PRECIOUS STONES. 47 



tourmaline, gold, garnet, zircon, etc. In the prairie washings the 

 diamonds occur in a conglomerate consisting of quartz fragments 

 covered with a thin bed of sand or earth. This deposit airords the 

 finest stones. Other Brazilian localities are those of Bagagem, at 

 which place a 247^ carat stone was found, and at Abaethe, Minas 

 Geraes. In Bahia diamonds are found at Lencaes; along the river 

 Cacholira, especially at Surua and Sinorca; they occur also on the 

 Salobro and other branches of the Pardo River. 



By far the greatest portion of diamonds now obtained come from 

 South Africa, their discovery dating from 1867. The diamond work- 

 ings are of two kinds, river diggings and dry diggings. The river 

 diggings are in the gravel of the Vaal River from Potchefstroom down 

 to its junction with the Orange River, and along the latter as far as 

 Hopetown, the principal workings being along the Vaal between Klip 

 Drift and its junction with the Hart River. The dry 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 approximately spherical 

 or oval in form, with an average diameter of some 300 yards, the 

 entire production 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 controls the diamond output of the world. Some 

 idea of the enormous output of the region may be gained from the 

 statement that from 1867 to 1887 over 33,000,000 carats, or more 

 than 6+ tons of diamonds were taken out, valued in the rough at 

 $225,000,000, and after cutting at $450,000,000. 



At the Kimberley mines the diamantiferous area is inclosed in a 

 wall of nearly horizontal black carboniferous shale, The upper 

 portion of the deposit consists of a friable mass of pale yellow color, 

 called the "yellow ground." Below the reach of atmospheric in- 

 fluences the rock is more firm and of a bluish green color; it is called 

 the "blue ground." This consists essentially of a serpentinous 

 breccia inclosing fragments of carbonaceous. shale, bronzite, diallage, 

 garnet, magnetite, etc. The diamonds are rather abundantly dis- 

 tributed through the mass, often to the amount of four to six to the 

 cubic yard. These areas are believed to be volcanic pipes, and the 

 occur] ence of the diamonds is obviously connected with the igneous 

 intrusive, either being formed by the action of heat upon the car- 

 bonaceous shales, or being brought up from underlying rocks. (See 

 pi. 14.) 



For a detailed description of these occurrences the reader is referred 

 to authoritative and comprehensive works like that of Mr. Gardner 

 F. Williams (The Diamond Mines of South Africa), or M. DeLaunay 

 (Les Diamants du Cap. Paris, 1897). Also reference should be 



