AND ASSOCI-iTED ROCKS OF THE SOUTHERN TRANSVAAL. 



431 



from the outcrop, the reef below is found to be 2 feet thick. Here, 

 as in the typical area, we find that} the strata have suffered con- 

 siderable disturbance. 



Pig. 8. — Diagram- section, east of Nigel Mimpaclit. 



a. Coal-bearing beds. 



b. Conglomerate-beds 



Eed slaty shale 



About 2 miles south of the Nigel Mine a reef, underlain by 

 shale, has been struck in the Eomola and Plorida Mines ; the dip is 

 south. The intervening ground between these mines and the jN'igel 

 is thus seen to be occupied by strata forming the summit of an 

 anticline. Unfortunately there are no exposures to be found. In 

 the section (fig. 7, p. 430) it is made to appear that the low dip can 

 be accounted for by denudation having removed the larger part of the 

 anticline. The schistose nature of the rocks, where these are not 

 decomposed, shows that disturbance has taken place. The ground 

 between the Nigel and Romola Mines is occupied by a valley, north 

 and south of which the strata gradually flatten out. 



Near Heidelberg, about 9 miles S.S.W. of the Nigel Mine, con- 

 glomerates and sandstone crop out, forming the rocky foundation 

 upon which the town is built. The same beds also compose the 

 hills lying behind it. In the town section the beds are almost 

 horizontal, but westwards the dip increases to an average of about 

 15^. On the eastern side of the town, however, immediately after 

 crossing the Bloesbok Spruit, the strata are observed to have a very 

 high dip. 



A little farther to the N.E., in the Marais-Nigel Mine, a reef 

 underlain by red shale, identical with that in the Nigel Mine, dips 

 at an angle of 30° W. These frequent changes of dip and strike 

 suggest very forcibly to the mind of the observer the fractured and 

 disturbed state of the country. 



The sandstones are exposed west of Heidelberg, along the 

 Johannesburg road, for about 2 miles, when they are covered up 

 by a quartz-amygdaloid lava. From this point westwards, all up the 

 Klip River valley — and how much farther it is impossible to say, — 

 the whole country is flooded by volcanic rocks. In one or two 

 places, however, as in the Black Eeef Mine, the quartzite-and- 

 conglomerate series comes to the surface with a very gentle southerly 

 dip. The writer had no opportunity of examining these beds 

 carefully. 



About 35 miles south of eTohannesburg, on the Kimberley road, 

 some high hills are composed of quartzite, dipping to the south at a 

 small angle ; but volcanic country soon comes in, and the strata 



2h2 



