THE GEOLOGICAL FORMATION OF GERMAN S.W. AFRICA. 337 



slate to a jasper are noticed. 



Here we find extremes meeting — as far as geological formations 

 are concerned. What a vast interval between the formation of 

 these rocks — to my mind far older than the other Archaean rocks 

 met with in other parts of South Africa — and the next formation 

 met with ! Lying directly on these old schists and granites is a 

 recent — we may say present day — formation, comprising the debris 

 of the lower rocks, of which little but the Quartz remains. Fel- 

 spars have been decomposed into clay, most of which has been 

 blown to the north, a little remaining to form small clay bands 

 here and there. Much the same thing has happened to the Micas, 

 but the white and coloured Quartz pebbles are met with in large 

 quantities, shifting about with the incessant winds and helping to 

 wear down the rock surface. 



In addition to the Quartz pebbles which form part of the present 

 day formation one finds debris of Amygdaloidal Diabase, namely 

 Agates and Chalcedony, sundry fragments of the local rocks and, 

 last but not least, Diamonds — the debris, one may say, from pipes 

 of " Blue ground." 



This mixture, forming the diamond bearing gravel, occurs in 

 the valleys and depressions and in smaller quantities scattered on 

 the higher ground. The valleys have been largely formed by the 

 eroding action of wind-blown sand and gravel. The rocks have 

 been scoured and scooped and pitted to a remarkable degree. 

 Boulders that have been partly imbedded in gravel have had the 

 unprotected portion worn right off. 



A good deal of the gravel is at present being solidified into a 

 coarse grit, the cementing material being Carbonate of Lime 

 derived from Archaean Dolomites and Limestones of which in- 

 numerable fragments are found lying in the gravel. Owing to 

 the infrequency of the rainfall any dissolved Carbonate is easily 

 redeposited. 



In places the solidification is not yet complete, and the rock can 

 be broken by scraping it with one's foot. In other places the 

 process is further advanced and a fairly hard rock has been pro- 

 duced, which is in turn being subjected to the degrading action of 

 the moving gravel. 



As the original gravel contained diamonds, the solidified mass 

 does too, and this has given rise to a statement that the original 

 matrix of the diamond had been discovered. 



This solidified gravel has, I find, been described as being of 

 Cretaceous age. This statement I could only accept if indisputable 

 evidence is brought that the deposit contains fossils which are 

 found in Cretaceous beds and not in more recent formations. The 

 fossils that I have observed are all present day sea shells, and the 

 reason for their being in their present position is a very simple 

 one. 



I had heard so much about the gravel being of marine origin, 

 as evidenced by the marine shells, observed miles inland, that I 

 naturally looked closely into the matter. True enough at many 

 places shells were found scattered amongst the gravel. These 

 were mostlv the shells of mussels and limpets — to give them their 



