28 Transactions of the South African Philosophical Society. 



sented by the Kimberley pipes, where the throat of the volcano is 

 plugged with a breccia, or hardened mud, in which a great variety of 

 rocks, granites, gneisses, mica-schists, slates, &c, besides the basic 

 eclogites, and even tree-trunks are found. 



The last named show clearly enough the small heat that must 

 have existed during the expulsion of the breccia mud, but it might 

 be argued that the trees only fell down into the mass after it had 

 cooled. Against this, however, we have the conclusive experiments 

 of Luzi who embedded diamonds in the Kimberlite matrix which he 

 kept heated to 1,770° C. for half an hour. On cooling the mass and 

 taking out the diamonds," he found these intensely corroded, 

 showing that the diamonds could not have been swirled about in 

 the magma in which they now are found, and which was once 

 molten, bub must have got into their present position while the 

 breccia mud was comparatively cold. The slight amount of 

 corrosion exhibited in most Kimberley diamonds was no doubt 

 caused by the action of the blue-ground; the original matrix, 

 however, from which the diamonds crystallised was in all probability 

 a metallic one, the amount of titaniferous iron ore in the blue, 

 pointing to the original matrix having been an alloy of titanium 

 and iron.f 



Chaper was so impressed with the absence of heat in the 

 Kimberley mines, the included blocks being unaffected, and the 

 rocks forming the sides of the chimney showing no trace of 

 metamorphic action, that he inclines to the view that the nearest 

 analogues of the outbursts that formed the Kimberley vents are 

 those that take place in petroleum regions. In the latter, through 

 the action of carbonic acid gas, at low temperatures, there occur 

 sudden bursts of mineral oil accompanied with sand, the latter 

 representing, as it were, the serpentinous mud of the Kimberley 

 breccia.]: 



In mid- Atlantic the recent voyage of the German South Polar 

 expedition in the SS. Gauss dredged quartz sand from the sea 

 bottom in lat. 32° 52" S. long. 13° 18' E. ; from a depth of 2,750 

 fathoms; the deposit has been described by Dr. PJailippi. § The 

 sand was entirely outside the area to which land detritus could be 

 brought, and the deposit was far too great to have been rubble 



* Uber kunstliche corrosionsriguren auf Diamanten, Berichte der deutsch. chem. 

 G-esell., Jahrg. 25, No. 14, Berlin, 1892, p. 2470. 



f See on this question, Moisson, " Comptes Kendus," cxvi., p. 292, 1893. 



} Bull, Soc. Geol. France, 3 erne series, torn. 19, pp. 313 and 944; also, Note sur 

 la region diamontifere de l'Afrique Australe, Paris, 1880, p. 42. 



§ " First Fruits of the German Antarctic Expedition," Nature, 1902, p. 224. 



