Parent-Rock of the Diamond in South Africa. 113 



ments obtained from more ancient crystalline rocks.^ The 

 " washings,"^ a parcel of which I received from Mr. 

 Trabenbach, also show that the boulders are really water 

 worn. Besides two unworn pieces of pyrite and a rough 

 bit of eclogite, about three quarters of an inch in diameter, 

 the pyroxenic constituent of which was a bright emerald 

 green (? smaragdite), I find part of a subangular fragment 

 of chrome-diopside associated with two or three flakes of 

 the usual mica, a well rounded garnet fully 0.6 inch 

 across, and half a well worn pebble of eclogite, about one 

 inch long and half an inch thick. The rounded water- 

 worn look of the great majority of the smaller constituents 

 (chiefly garnets and pyroxenes), about the size of hemp 

 seed, is very obvious. I had suspected some of the grains 

 washings from the De Beers Mines to have been similarly 

 treated ; but here it is indubitable, indeed many of the 

 dark green specimens are so smooth outside that they 

 could only be identified after fracture. The ordinary 

 diopside can, however, be recognized, with some of a 

 clearer and brighter green. Most of the garnets are 

 pyropes, but a few resemble essonite. I find also some 

 grains of iron oxide and of vein quartz. Thus, the presence 

 of water-worn frag;ments, large and small, in considerable 

 abundance, shows the " blue ground " to be a true breccia, 

 produced by the destruction of various rocks (some of 

 them crystalline, others sedimentary, but occasionally 

 including water- worn boulders of the former) — i.e., a result 

 of shattering explosions, followed by solfataric action. 

 Hence the name Kimberlite must disappear from the list 



1 As these eelogites are very coarsely crystalline, we are justifled in assuming they 

 were once deep-seated rocks, and so much more ancient than the date of tlie conglom- 

 erate. To prevent any ;nisunderstauding, I may repeat that the matrix from which 

 these boulders were taken (at various depths, from nearly 100 to about 300 feet) cannot 

 be any alluvial deposit, but is the typical "blue ground," practically identical with 

 that in the Kimberly mines. 



2 The name is given to the mineral residue left after washing away the decomposed 

 matrix of tlie "blue ground." 



