430 



MR. W, GIBSOIf ON THE GEOLOGY OF THE GOLD-BEARING 



folds, and afterwards pierced in all directions, and often overflooded 

 b}^ igneous rocks. 



It has been previously mentioned that the reefs are cut off to 

 the east near Boksburg by a mass of diorite, and that they come to 

 the surface again, about four miles to the N.N.E., in the Chimes 

 and Yan Ryn properties (see Map, PL XI.). A true conglomerate 

 with associated quartzite is here exposed, the strata striking nearly 

 due north and south, and dipping to the west. 



The conglomerate-beds also crop out about 15 miles S.S.E. of 

 Boksburg, and are worked for gold in the JS'igel and adjoining 

 properties. In the Nigel Mine (see fig. 7) the lowest reef is under- 



Pig. 7. — Section across Nigel and Romola Gold-mines. 



[Length of section about 2^ miles.] 



a. Coal-bearing beds. I c. Slaty shales. 



h. Conglomerate-beds. | d. Kigel Eeef. 



Between the points xx the country is grass-covered. 



lain by red shale, about 60 feet thick ; while the bed immediately 

 above this reef is sandstone. The reef has an average thickness 

 of 2 feet. Traced downwards the underlying rock approaches 

 more and more in character to a slate or schistose rock, while the 

 sandstone above it changes into a quartzite. The dip is 30° N. ; the 

 strike due east and west. The dip of the overlying conglomerates 

 gradually decreases northwards, till in about a mile they become 

 perfectly horizontal. Traced westwards the strike of the beds 

 gradually assumes a southerly trend, while the dip is eastward. 

 In the Reraboro, Lavers-Nigel, and other properties towards the 

 east, the Reef series changes its strike to a northerly one, the dip 

 being then westward. Evidently the strata have been folded to 

 form a basin. 



In the eastern portion of the Nigel Mine and in the adjoining 

 properties the reef is very thin. In the Lavers-Mgel a shaft sunk 

 in the associated shale showed that this becomes intensely hard and 

 schistose lower down, the usual red surface-colour changing to blue. 

 The soft nature of the shale at the surface is due to oxidation. The 

 banding and colouring in these oxidized shales are marvellous, tints 

 from the brightest red to the dingiest brown, with deep and light 

 blues streaked with orange and gold, predominating. Some of the 

 colours may justly be likened to the cloud-colourings of an autumn 

 sunset. 



The reef at the surface is in all cases very narrow; but in a 

 shaft sunk quite recently on the Remboro property, at some distance 



