TnANSACTIOXS. 199 



the small mine, St. Augustine's, near the Central. Though this 

 may be the result of a lateral thrust, it seems more simply ex- 

 plained as the result of volcanic action. Hence if we suppose the 

 above reasoning correct, the period of formation of the craters is 

 fixed as the epoch of the deposition of the Kimberley shales by 

 the occurrence of this dolerite contemporaneously with the shales. 

 The next point of interest is to know whether the diamondi- 

 ferous blue earth occurs really t?i situ or has been washed in from 

 above. I am strongly inclined to the latter view, and for the 

 following reasons : 



1. The blue earth has no distinctively igneous appearance 

 whatever. 



2. Though in the case of St. Augustine's Mine the part of the 

 blue near the edge of the pit is hardened, there is generally no 

 sign of the blue having been ejected from below, and it certainly 

 does not alter the rocks with which it is in contact. Usually 

 speaking, those parts of the blue earth which are in contact witli 

 the surrounding strata are marked by a soft jumbled or " soapy " 

 condition. 



3. Mr G. R. Lee, of Kimberley, shewed me a piece of lignite 

 found in the blue earth, and he also told me that he had found 

 limestone shells apparently unaltered in the blue earth. 



It appears therefore very probable that the blue earth has 

 simply been brought in from above. There are even many reasons 

 which tend to shew that the whole of the craters were subaqueous. 

 The Kimberley shales have all the appeaiance of a deposit formed 

 in deep and quiet water. One must also remember that they form 

 the starting point of the fresh water beds of the Caroo formation 

 and the Stormberg Beds (sandstones and coalmeasures), all of 

 which are distinguished by a remarkable horizontality of the strata, 

 and which attain a thickness of 2000 feet on an average. A glance 

 at the map of South Africa shews a gigantic mountain chain 

 within 80-120 miles of the coast and rising to an average height 

 of 7000 feet above the sea. This range (the Drakensberg) includes 

 such mountains as the Font aux Sources, 10,000 feet; the Giant's 

 Castle, 9657 feet; and Cathkin Peak, 10,357 feet. Now Kim- 

 berley is only 4200 feet above the sea. The basin of the Vaal 

 River in fact is bounded by the Drakensberg, then by a continuous 

 series of mountain ranges, under difierent names (Stormbergen, 

 Bamboesbergen, Kikvorschbergen, Nieuwveld, Roggeveld, Guaap, 

 &c.), which run all round the southern corner of the continent at 



