The Volcanic Fissure under Zuurberg. 



193 



tion. The lava in this wide portion of the fissure varies consider- 

 ably ; it is usually very full of amygdales, or it is vesicular owing to 

 the infilling substance having been removed, but at places it becomes 

 nearly compact. The relationship of the lava to the tuff in this 

 locality, as in others to be mentioned below, is difficult to ascertain 

 for want of outcrops, but on a part of the ridge near the south-east 

 boundary of Slag Boom I was able to make the plan shown in Fig. 2. 

 There is one general rule concerning the relationship of the two 

 kinds of rock, tuff or breccia and lava, which fill the fissure ; pieces 

 of lava do not occur in the fragmental rocks, but pieces of the tuffs 

 are often enclosed by the lava. In Fig. 2 it is obvious that the lava 

 forms vein-like bodies in the tuff. On Slag Boom the volcanic 

 fissure following the fault bends nearly north-west before again 

 taking a westerly course through the Enon Mission ground. The 

 height of the volcanic rocks at the top of the Kremlin-Slag Boom 

 ridge is about 800 feet above the White Biver on Slag Boom, and 

 the position of the volcanic fissure appears to be practically vertical 

 (Fig. 3). I have not followed the rock westwards beyond Enon. 



LOT 15 



Fig. 3. — Section through Slag Boom, about 3J miles. Vertical and horizontal scale the same. 

 1. Witteberg beds. 2. Lower Dwyka shales. 3. Dwyka conglomerate. 

 4. Volcanic rock. 5. Enon conglomerate. 6. Shales, &c, of Uitenhage beds. 



Throughout this part of the fissure's course the rock to the south is 

 almost certainly Enon conglomerate, though the actual contact has not 

 been seen. The conglomerate country is always marked by a change 

 of character in the soil, which becomes brighter red in colour and 

 more or less heavily charged with rounded pebbles and boulders of 

 quartzite derived from the conglomerate. Where exposures occur, 

 as on Enon, the track from Slag Boom to Coerney, and the Zuurberg 

 Pass road, the nearest rock to the lava on its south side is the 

 ordinary red Enon conglomerate. 



Turning now to the country east of the Zuurberg road, the 

 volcanic rock trends about E. 10° S. towards the Coerney Biver, but 

 beyond ascertaining the presence of the lava along this line I did 

 not follow the fissure across this dense bush countiy. The lava 

 itself seems to come to an end about a mile from the Coerney Biver, 

 for I could find no trace of it in that valley or on the hill just to the 

 west, where it should be seen if present. In the bed of the Coerney 

 Biver, just north of the boundary between Buffel's Kuil and Coerney, 



