60 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [May 1 894, 



randt district, with their associated quartz and shales, form one 

 series, which has undergone a considerable amount of metamorph- 

 ism. This series is much newer than the crystalline rocks on 

 which it rests, since the gold-bearing conglomerates have been 

 formed mainly at the expense of the underlying . granites and 

 gneisses, which are largely threaded with auriferous quartz-veins. 

 As regards stratigraphical arrangement, the entire series associated 

 with these gold-bearing beds has been thrust over the gneisses. 

 Consequently, the beds do not seem to be contained in a simple 

 basin ; but, as was pointed out by Prof. Lapworth, it is probable 

 there has been overthrusting and shearing along the edges of the 

 basin, and possibly repetition in its interior, so that the actual 

 thickness of the beds may not be very great. Mr. Gibson observes 

 that subsequent to these movements the strata were injected 

 with basic igneous material, and much of the country was flooded 

 with lavas of a similar character. 



Mr. Attwood, who has had considerable experience in gold-fields 

 and their surroundings, stated that this district bore no resemblance, 

 geologically speaking, to anything hitherto discovered and was 

 therefore of special interest. He did not think that the gold in 

 the quartzites and conglomerates could be called alluvial gold, as 

 suggested by Prof. Green, because the metal is reported to be found 

 in a fine state of division, whilst in all true alluvial deposits it 

 is found of various forms and sizes. On the whole, Mr. Walcot 

 Gibson was somewhat reticent as to the origin and method 

 of deposit of the gold, but Mr. Alford stated his opinions on these 

 points rather more freely, whilst allowing that the subject was 

 an intricate one. The gold, he said, occurred in the matrix of the 

 conglomerate and seldom in the quartz-pebbles, and, although the 

 conglomerate-reefs were by no means regular in gold-bearing 

 value, that value appeared to be greater where the beds had a high 

 angle of dip and were in proximity to intrusive igneous rocks. 

 For a further expression of Mr. Alford's views on this curious forma- 

 tion reference may be made to a work of his which has been lately 

 published. 1 As it is admitted on all sides that the Witwaters- 

 randt Series is one of exceptional character, I may be pardoned for 

 having dwelt upon the subject at some length. 



African geology has been further enriched by an interesting 

 communication from Prof. Valentine Ball ' On some eroded Agate- 

 pebbles from the Soudan,' which were collected by Surgeon-Major 



1 ' Geological Features of the Transvaal,' London : Stanford, 1891. 



