(If 1 X'-i'-l<i,i<l* Itii'inoii'l Mini v, Grriqualand fFW. 481 



that some of the deeper-seated specimens from the I)e Beers Mine, 

 though Belonging to the typical mass of kimberlite, are hardly less 

 rich in the secondary mica than this one from Xewlands, so that 

 from the chemical point of view, apart from other considerations, the 

 propriety of classing " kimberlite '' with the (altered) peridotites is 

 worse than doubtful. 



The rock fragments are often about O'l inch in diameter, though 

 pieces nearly half an inch across also occur, sub-angular to rounded in 

 form. The majority represent varieties of basalt, some apparently 

 retaining traces of a glassy base, others rather minutely holoerystal- 

 line. They show signs of alteration, but nothing in their structure or 

 composition calls for any detailed description. It is difficult to deter- 

 mine the exact nature of the light-coloured fragments. The green 

 mineral is sometimes a granular augite, rather decomposed, sometimes 

 an actinolite ; the lighter (dominant) part often effervesces briskly 

 with HC1, and calcite is seen under the microscope, associated with a 

 grey decomposition product, which often suggests the former presence 

 of a felspar. In one case a holocrystalline granular structure is clearly 

 seen, and the ieplacing mineral has some resemblance to pseudophite. 

 Hence I consider these fragments to represent a plagioclase-augite 

 rock allied to gabbro, and related to the boulder already described. 

 Its presence, and the comparative abundance of bits of basaltic rock, 

 seem to be characteristic of the locality. 



One specimen, however, calls for a little notice. Part of it re- 

 sembles a compact mudstone ; the rest, about an inch across, is rather 

 decomposed blue ground ; the outer side of this suggesting that, as in 

 the case of a specimen described last year, the " blue ground " may 

 occupy a fissure in the " country rock." On microscopic examination, 

 however, this proves to be doubtful. The apparent outer surface is 

 only a vein product, consisting of a fibrous mineral, possibly arragonite, 

 associated with a little actinolite. The seeming mudstone is more like 

 a very decomposed igneous rock, probably a rather felspathic lisalt. 

 The " blue ground " is also much decomposed, the mineral fragments 

 being converted into a pale greenish-yellow fibrous material, much of 

 which is actinolite. A fragment of basalt (not identical with the other) 

 appears to be altered for a depth of not quite one-tenth of an inch 

 from the exterior, for in this part small distinct flakes of brown mica 

 are scattered about. 



The specific gravity of a specimen of "blue ground," rather harder 

 than the rest, was 2'667 ; two others, representing the most brittle 

 vai-iety, were weighed, but as each crumbled a little when immersed, 

 the results are slightly too low. One (the better) was 2-622, the other 

 2'614. I tried the former a second time, but as it broke up more readily 

 than before, abandoned the attempt. 



I referred last year to a pyrope in which diamonds were embedded. 



VOL. LXVII. 2 M 



