THE GENESIS OF THE DIAMOND. 197 



from a conglomerate reef similar to the Witwatersrand reefs. It 

 had occurred to me that either the wash from a diamond-bearing pipe 

 had been mixed with the detritus when the conglomerate beds were 

 formed or that a diamond-bearing dike penetrated the conglomerate 

 strata and its contents were mined and sent to the mill along Avith 

 the gold ore. This remarkable occurrence of diamonds has been 

 explained to me by an old Kiml>erley miner who was on the ground 

 {it the time the diamonds were found. 



In his opinion some of the top soil or wash was mined with the 

 gold-bearing conglomerate and the diamonds came from this alluvial 

 deposit. The finding of these diamonds in the battery mortar, as 

 above described, is well authenticated. The diamonds were of a 

 greenish color. 



In November, 1902, the Premier mine near Pretoria, Transvaal, 

 was found. The surface area of the mine has ;^),515 claims (a claim 

 being 31 by 31 feet) ; l,'28r) of these had been worked to an average 

 depth of 38 feet at the end of 1905. This ground has proved to be of 

 exceptional richness and has yielded 1,821,609 carats from 2,824,579 

 loads of 1,<U)() pounds each. It was in this mine that the Cullinan 

 diamond, famous for being the largest diamond crystal known, was 

 found January 26, 1905. This stone is of excellent quality and 

 weighs 3,025f carats — 9,586.5 grains (1.3T pounds). 



During last year (1905) a piece of Brazilian boart or carbonado 

 weighing 3,078 carats was broken up and sold in London. 



Coming noAv to the occurrence of diamonds at Kimberley, I may 

 preface my remarks by saying that my experience with the mines at 

 Kimberley dates back nearly twenty-two years, about nineteen of 

 which have been passed in the management of tliem. 



The diamonds occur in a rock commonly known as '' blue ground," 

 filling the craters of extinct volcanoes. This rock was described by 

 Prof. Henry Carvill Lewis as a pori)hyritic volcanic peridotite of 

 basaltic structure ", which he named " kimberlite." It must be desig- 

 nated as breccia. There is no doubt that the blue ground is of vol- 

 canic origin, and Avas forced up from below ; it consists of olivine 

 with fragments of other rocks. I am of the opinion that the craters 

 were filled by aqueous rather than igneous agencies, possibly by 

 something in the nature of mud volcanoes. 



It is a noteworthy fact that all the craters were filled just even with 

 the surface of the surrounding country. Would this have been the 

 case if the pipes were of igneous origin ? I think not. 



It may be claimed that the surface of the country, as it existed 

 when the craters were filled with the diamond-bearing breccia, was 



o The Matrix of the Diamond. Henry Carvill Lewis, M. A., F. R. S., at a meet- 

 ing of the British Association at Manchester, August and September, 1887. 



