ANB ASSOCIATED KOCKS OF THE SOUTHERN TRANSVAAL. 417 



cidedly opposed to the theory that the conglomerate-beds lie in a 

 simple basin. 



(a) Second Reef SeHes, south of the Main , Meef — There are some 

 conglomerate-beds struck by the diamond drills which, so far as 

 position is concerned, lie nearest to the Main E-eef on the south, 

 but these do not apparently come to the surface. 



Two conglomerates caUed the Red and Yellow Eeefs crop out, 

 however, about a mile to the south of the Main Reef Series. The 

 Red Reef is best seen in the Great Britain and Kimberley Roode- 

 port Mines, situated about 9 miles west of Johannesburg ; while 

 east of Johannesburg both the Red and Yellow Reefs can be studied 

 near Elsburg and Boksburg. 



The outcrop of these reefs cannot be traced for any great dis- 

 tance, being generally hidden beneath the ubiquitous, superficial red 

 soil. Where seen, their dip is always lower than that of the Main 

 Reef Series, but proportional to it. As these reefs are not mined 

 to any great depth it is impossible, from the limited nature of the 

 observations, to state exactly what their composition is. Judging 

 from surface-outcrops, they are unlike any one of the members of 

 the Main Reef Series. The cementing-material of the reefs is much 

 softer, and quartz-pebbles are rarer ; while white and grey quartz- 

 ites, together with black speckled sandstones, are very common. 

 The associated rocks are grits and sandstones. 



(b) Third Reef Series, still farther south. — The next well-marked 

 conglomerates crop out about 5 miles south of Johannesburg, and 

 form a line of escarpment facing the north. They are mined in 

 only one or two places, and, excej)t in the case of the Aurum Mine, 

 never to a sufficient depth to reach the undecomposed strata. 

 There are several of these conglomerates, and they are associated 

 with grits and sandstones. In a shaft on the Aurum estate (see 

 Map, PL XI.) the sandstones are found to assume more and more 

 the character of quartzites, and to become slightly pyritous as they 

 are traced downwards. The pebbles in the conglomerates are very 

 much larger than in any of the reefs to the north — the pebbles 

 averaging about 3 inches in diameter, while some are as large as 

 a man's head. They are nearly all of a pure white quartzite, a 

 few being of sandstone. 



These conglomerates can be traced along the escarpment for about 

 15 miles, east and west. In the direction of the dip they are soon 

 cut off by an immense outflow of basaltic and quartz-amygdaloid 

 lavas, forming the heights called the Eagle's jSTest (see Map, PI. XI.). 

 Along the whole line of strike the conglomerates have a uniform 

 dip of 15° S. This is an interesting point, for north of a line 

 drawn up the Klip River valley the strata are affected in the same 

 manner, as to dip, as the Main Reef Series ; while the conglomerates 

 now under discussion, and the associated rocks which lie to the 

 south of this line, are uniform in dip and strike for the whole dis- 

 tance mentioned above. It is thus probable that a fault runs up 

 the Klip River valley. This hypothesis is further strengthened by 

 the fact that the material thrown out at the surface of the ' Klip 



