410 GOLD-BEAEING EOCKS OF THE SOUTHEEN" TEAlSTSYAAL. 



2. The Main Reef Series. 



(a) The Type-sections of the Main Reef Series in the Salisbury and 

 Henry Nourse Mines. 



As it is impossible for the geologist to locate his position definitely 

 in the Witwatersrandt conglomerate series, and as neither the 

 summit nor the base of this group of strata has been discovered, he 

 is driven to take some arbitrary starting-point. It is most con- 

 venient to begin with the line of conglomerate-bands which have 

 been opened up by the various gold-mines. The sections are com- 

 plete, and the data, if ordinary care be exercised in selecting them, 

 are reliable. 



(1) The Salisbury Gold-mine is situated almost in the centre of 

 the line of conglomerates, and shows very clearly the relationships 

 of the beds to each other. The strata are very little metamorphosed 

 and only slightly disturbed by faulting ; and the mine is well opened 

 up, so that a complete section can be obtained. 



The conglomerate-beds and the associated rocks make no appear- 

 ance at the surface, their outcrop being concealed beneath the super- 

 ficial red soil. The mine is worked by two levels at a depth of 

 66 feet and 130 feet respectively. Both levels give a very instructive 

 section from north to south of nearly 150 feet in length. The dip is 

 high — 85° S. ; the strike due east and west. The dip remains con- 

 stant throughout the mine and on both levels. On the upper level 

 a ' cross-cut,' north and south, near the western boundary of the 

 mine passes through the sequence of strata, beginning at the north, 

 enumerated in the explanation of fig. 1 facing this page. 



The four conglomerates (c, e, g, j) are collectively termed the 

 Main Eeef Series. On Wyld's map of the Witwatersrandt Gold- 

 fields (1888) and in the map accompanying the present paper 

 (PI. XI.) this Main Eeef Series is represented as one bed, the scale 

 in both cases being too small to admit of the separate beds being 

 shown. 



The word ' reef ' must not be taken in its ordinary meaning ; the 

 reefs are not veins in any sense, but are true conglomerate-beds. 

 The term 'banket' is often applied in the district to any conglo- 

 merate-bed whether it contains gold or not, and a series of sand- 

 stones and conglomerates is often spoken of by Afrikanders as a 

 ' banket formation.' 



The four conglomerate-reefs are strikingly similar in appearance, 

 though a miner who has worked for any length of time in any one 

 mine recognizes distinct differences between them. 



The Main Beef proper, in the Salisbury Mine, and indeed in most 

 of the other mines, is the thickest and least coherent of the series. 

 The pebbles are numerous and of all sizes, varying from half an inch 

 to two inches in diameter. They are chiefly of milk-white quartz, 

 very much broken ; but others, formed of a yellow talcose material, 

 looking something like hardened clay, are not uncommon. The 

 cementing-material, or that in which the pebbles are embedded, is 



