AITD ASSOCIATED EOCKS OF THE SOTJTHEEIs^ TEAN'SVAAL. 423 



occupying the ground between the Main Eeef Series and the 

 Quartzite-and-Shale Grouj) are everywhere found to have the same 

 dip as the Main Eeef Series. It has also been ah'eady stated that 

 the quartzite bands die out eastwards against a fault. There cannot 

 therefore be any doubt that a fault separates the Main Eeef Series 

 and its associated beds from the Quartzite- and-Shale Group below. 

 The strata occupying the ground between the outcrops of the two 

 groups are composed of lenticular bands of sandy quartzite, compact 

 quartzite, and red shales. It will be seen, on referring to the Map 

 (PI. XI.), that the beds composing the Quartzite-and-Shale Group 

 keep the same relative distance from the Main Eeef Series from 

 Johannesburg to the Banket Mine on the west, and to the Jumpers 

 Mine on the east. Evidently the two groups form portions of one 

 larger series, but the exact sequence and relationship of the beds 

 cannot be fully made out, owing to the break occasioned by the 

 fault. 



B. Physical Eelatioxships oe the Witwateesea]st)t Eocks. 



1. Relation of the Loiver Quartzite-and-SJiale Gron/p to the 

 underlying Rocks. 



The rocks underlying the entire series of quartzites and shales 

 already described are found to consist of highly crystalline and 

 metamorphosed beds, which have been intensely crumpled and 

 plicated. The nearest approach to an absolute junction between 

 the two sets is found on the Houghton Estate (see Map, PL XI.). 

 It has been previously mentioned that a tunnel driven into the 

 fourth ridge of quartzite passes first of all through some highly 

 metamorphosed shales. In a vertical shaft, a little to the north, 

 gneissic rocks were struck at a depth of about 30 feet ; the ground 

 between the mouth of the tunnel and the shaft is quite flat. Small 

 isolated patches of an intensely hard and highly schistose quartzite 

 are found in several localities north of the Houghton Estate, In 

 one or two places these patches can be seen to overlie gneissic rocks, 

 but any absolute junction of the two could not be discovered. In 

 one spot, about 3 miles north of the manager's house, a smaU boss 

 of pegmatite crops out. The crystals of quartz in this are some- 

 times 3 inches long and about ^ in. across. The felspar is of a faint 

 pinkish-white colour, the crystals being sometimes very large. The 

 exposure is not sufficiently extensive to show whether this coarse 

 granite is intrusive. To the east, and not more than 200 yards off, 

 a dyke of fresh-looking diorite is found with a north-and-south trend. 



In the main shaft of the Houghton Gold-mine a vein of quartz 

 enclosed in quartzite suddenly dies out, at a depth of about 60 feet, 

 against a pinkish-red granite. It was stated by the manager that 

 the quartz-vein and the associated rock commence with a southerly 

 dip, which considerably decreases in amount to the south, till finally 

 the rock becomes horizontal, and then assumes a northerly dip till 

 it ends off against the granite. It is to be noted that the nearer the 



