558 Gregory — Diamonds in South Africa, 



into a clean white sand, which hereabouts is a member of the drift. These meres 

 appear, then, to be of the character of tarns, formed (as I believe with Professor 

 Ramsay, true tarns have been) by ice, which in this case has moved from all'sides 

 towards the spot occupied by the mere,'where its accumulation has produced a greater 

 erosion, and thence taking the direction of the present outlet, commenced the exca- 

 vation of the valley. 



Such depressions in other districts have no doubt existed, but have become filled 

 up and masked by lacustrine deposits. In Norfolk the glacial condition has lasted 

 longer, and the original hollows remain. 





IV. — Diamonds from the Cape of Good HopH. 

 By James R. Gregory. 



WEEE the diamonds said to be found at the Cape, and Sent to 

 England, really found in South Africa ? I have just returned 

 from the so-called diamond district, to which country I proceeded 

 from England, being deputed by Mr. Harry Emanuel, the diamond 

 merchant, of Bond-street, who is well known as a most indefatigable 

 scientific enquirer on the subject of precious stones, and who naturally 

 felt a great desire to develop a new source of supply of a commodity 

 in which he is so largely interested. During the time I was in South 

 Africa I made a very careful and lengthened examination of the 

 district where the diamonds were said to have been found, but saw 

 no indications whatever that would warrant the expectation of 

 the finding of diamonds, or of diamond-bearing deposits, at any of 

 the localities. 



The geological character of that part of the country renders it 

 impossible, with the knowledge we at present possess of the diamond- 

 bearing rocks, that any could have been really discovered there. 

 The whole of the district from Cradock, almost in a direct line to 

 Hopetown, upwards of 250 miles, is composed of igneous or volcanic 

 rocks ; the huge piles of rounded boulders are Trap porphyries, and 

 the Trap dykes in many places that have forced them up, and the 

 sands both of a white and red colour, are simply the debris 

 from the breaking up and wearing away of those burnt porphyries 

 and burnt clays, or Porcellanite, which were formed originally 

 through the volcanic heat vitrifying these siliceous clays. No other 

 geological deposits are visible, nothing but igneous and volcanic 

 rocks, and the sands mainly produced by their decomposition, and 

 associated with these sands and in the beds of the Orange and 

 Vaal Rivers are the characteristic Trap minerals only — such as 

 Zeolites, Natrolite, and sometimes Stilbite, with small agates and 

 geodes of chalcedony, from the interior of which geodes, but of larger 

 dimensions, are derived the brilliant rock crystals of which thousands 

 may be found, most of them I'ounded on the edges, though some are 

 perfectly uninjured, as the usual hexagonal prism, sometimes with 

 both terminal pyramids. 



As further proof of the great antiquity of these volcanic rocks, 

 in a river bed about thirty yards in width, a tributary of the Vaal 

 Eiver, near the junction of the Orange and Vaal Eivers, I observed 

 some very large boulders of Trap, some three or four feet in diameter, 



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