VOLCANIC PIPES 363 



in adjacent mines or even in different parts of the same 

 mine. The extremely high proportion of pipes in which 

 diamonds are either scarce or entirely absent leads one 

 to the conclusion that the presence of the diamond in 

 the blue-ground must be regarded as almost accidental ; 

 it also shows that the parent rock of the diamond must 

 be rather sparingly and unevenly distributed in the 

 earth's crust. 



Some geologists, however, still incline to the view 

 that the diamond has crystallised out of the kimberlite 

 magma itself ; they consequently regard the eclogites as 

 segregations from the eruptive material. 



The alteration of the breccia after its intrusion into 

 the condition known as blue-ground was most probably 

 accomplished by ascending heated waters. The olivine 

 and enstatite, more especially the former, and also, but 

 to a lesser degree, the diopside, have been changed into 

 pale greenish serpentine together with a small amount 

 of calcite and iron ores. At the same time apophyllite, 

 natrolite and other zeolites have been deposited as 

 crystals accompanied by calcite, barytes, pyrites, and 

 marcasite. 



From the foregoing description of the breccias and 

 other rocks filling the pipes and fissures we see that 

 though they may differ widely in composition and 

 character, yet there are usually to be found connecting 

 links between one type and another. 



Had the Spiegel Kiver melilite basalt (alnoite) been 

 the only example of this type of rock known in the 

 Colony it would have been rash to have postulated any 

 connection between it and the contents of the Kimberley 



