182 T. G. BONNE Y [sept. 1899 



Discharges of lava occurred during the Karoo period and probably 

 afterwards (for both the pipes and the surrounding sedimentary rocks 

 are pierced by dykes), while the marked changes in the matrix of the 

 blue ground (what has been one of the great difficulties in determining 

 its real nature) suggest that for a long time it w r as acted upon by 

 water at a high temperature. Thus the volcanoes did not go beyond 

 the sol f atari c stage. They occur over a rather extensive district 

 and are fairly numerous — comparable, in fact, with the volcanic necks 

 of Fifeshire. 



The diamantiferous boulders obviously have no connection with any 

 existing alluvia. Probably they have come from a conglomerate at the 

 base of the sedimentary series, resting directly on the crystalline floor. 

 Thus far we have no means of determining what the age of the latter 

 may be, but the Dwyka conglomerate of South African geologists — 

 generally assigned to the Permian system — very probably extends 

 beneath the Karoo beds of the diamantiferous region, and may 

 repose on the crystalline floor. On that point, however, we must 

 await further evidence ; suffice it to say that the genesis of the 

 diamond in South Africa was not a phenomenon of Mesozoic or 

 later times, but must be yet more ancient. 



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