56 ORIGIN OF RAXD r.AXKETS. 



Bokkevelcl were, but fortunately a number of fault-ipits were 

 formed, which let down portions of these Cretaceous beds in 

 basins surrounded with rims of harder, older rocks. Thus por- 

 tions of the Uitenhage Series have been preserved. That the 

 deposit was originally continuous we know from the fact that 

 from fault-basin to fault-basin the rocks are, to all intents and 

 purpose*, identical. 



The main interest in the Enon Conglomerate in South Afri- 

 can geology is that we have a fluviatile deposit between 500 and 

 600 miles long and some 200 miles broad ; there is no difficulty, 

 then, in ascribing the Rand Banket to fluviatile origin, which at 

 most covers an area of 180 miles long by 80 broad. In the 

 -case of the Rand we must suppose that the four granite bosses 

 •of Potchefstroom, Johannesburg, Parys and Heidelberg form 

 the cones of mountains which towered above the plains in the 

 pre-Witwatersrand days. The first two are more interesting to 

 us, as the gravels washed down from these mountains are now 

 highly auriferous, while the gravels round the sockets of the 

 southern mountains have not yet been proved to contain payable 

 gold. The rocks above the granite were what we now call the 

 Swaziland schists, in those times probably little more metamor- 

 phosed than the beds of the Cape formation are now. If they 

 contained ore-veins, the gravels near their bases would contain 

 these ores as natural products of disintegration. Why gold is 

 precipitated in gravels and not in finer sediments is a question 

 not yet properly explained, but the fact remains that if the 

 country rock contain but the most exiguous traces of gold, the 

 rivers — large ones like the Irrawaddy and Rhine, or small ones 

 like the Homtini at Knysna — carrying the gold do deposit it 

 in the gravel patches. It might be advanced that the granite 

 should show traces of these ore-veins which are supposed to 

 have existed in the schists above them. This, however, is a 

 question that has only to be answered for those who believe 

 in Posepny's theory of the ascent of mineralising waters from 

 below ; on Sandberger's lateral secretion theory, the gold or other 

 metals would find their way into the ore-veins by solution from 

 the country rock and passage of the solutions into the open 

 spaces and crevices where the water relieved from pressure de- 

 posited the ore and gangue. To the Ascensionists the reply is 

 that the granite which shows no traces of gneissose structure 

 would be, when it was intruded, in a liquid state — that is. in a 

 condition in which pressure was communicated equally in all 

 directions^and therefore the crystals developed without re- 

 ference to any guiding directions ; hence the passage of 

 mineralising solutions would be accomplished through the mass 

 of the rock, without being restricted to* definite channels, and 

 without leaving any traces behind. It is unfortunate for South 

 Africa that the Enon gravels are mostly derived from the disin- 

 tegration of comparatively young rocks, which have not been 

 mineralised, so that the Enon gravels are barren in regard to 

 their gold content; but more recent gravels liave been formed 



