CATALOGUE OF GEMS. 505 



diamonds are rather abundantly di,stri])uted through the nia.s.s, often 

 to the amount of four to six to the cubic 3'ard. These areas are believed 

 to be volcanic pipes, and the occurrence of the diamonds is obviously 

 connected with the igneous intrusive, either being formed by the action 

 of heat upon the carbonaceous shales, or being brought up from under- 

 lying rocks. 



In this connection De Launay ' treats of the occurrence and origin 

 of the Cape diamonds as follows: He describes the serpentine of the 

 Kim])er1y mines as being derived from a peridotite determined as a 

 picrite-porphyry. Mixed with the serpentine are abundant fragments 

 of various rocks, so that many specimens are of the nature of a contact- 

 breccia. The serpentine bodies occur as pipes extending downward 

 in a nearly vertical direction to an unknown depth. In following the 

 volcanic pipes down it has been proved that each one passes through 

 .several formations. At the surface the inclosing rocks are carbo- 

 naceous shales, and at one time it was believed that the crystallized 

 carbon was primarily derived from these shales. Underlying these 

 shales is a bed of diabase. The serpentine at this horizon still con- 

 tained diamonds. Below the diabase horizon are quartzites, through 

 which the miners are now engaged in working. According to De 

 Launay. the inclosing terranes have had no influence on either the 

 quantity or quality of the diamonds. He therefore holds that the 

 diamonds have comfe from below with the peridotite-breccia and that 

 the diamonds did not originate in the Upper Carbonaceous shales. He 

 believes that since the cavities which contain the serpentine pipes are 

 in the nature of volcanic chimneys, water, penetrating to the contact 

 of a molten metallic bath charged with various carl)urets, caused the 

 sudden formation of carburets of hydrogen, and by their explosion 

 the opening of the volcanic chinmeys. The water produced the scori- 

 fication of the molten peridotite magma, and b}' the compression thus 

 exercised on the carbon, the crystallization of the diamonds. Finally 

 water accompanied the eruption of the peridotite and caused its ser- 

 pentinization. 



Diamonds are mined in the Urals, where they were discovered in 

 1829. The}' occur in the gold washings of the detritus along the Adolf- 

 skoi Creek, near Bisersk. and elsewhere along the western declivity of 

 the Uralian range. In Australia they are found in the alluvial of the 

 Cudgegong River, near Mudgee, and in the valley of the Horton River, 

 in the Bingera district of New South Wales. 



A few crystals have been occasionally met with in the United States 

 in Rutherfor^^, Franklin, Mitchell, and McDowell counties, Tsorth 

 Carolina: in Hall County, Georgia: in Kentucky, Ohio. Wisconsin, 

 Colorado, and Idaho, and in the ])lacers of P^ldorado, Amador, Nevada, 



^ Les Diamants du Cap, Paris, 1897. 



