TJie Transkei Gap. 69 



become an intensely hard quartzite. Mr. McKay, in tlie paper 

 above referred to, calls this quartzite a boss of " trachyte," a mistake 

 as to the nature of the rock often made in other parts of the colony, 

 especially when the quartzite forms a level covering to a hill like the 

 sheets of dolerite. At the time when the rivers were meandering 

 across the plain now so deeply cut into, the Gap-valleys were 

 probably not in existence, as the dykes which have since given rise 

 to them would have been denuded no deeper than the surface of the 

 river plain ; but when the land rose, and the rivers again began to 

 deepen their channels, certain of the minor streams took the course 

 followed by the dioritic dykes, as these offered the least resistance 

 to the erosive forces of the weather and the streams. The direction 

 of the N'Debe Gap-valley is at first due east, but after a few miles it 

 turns sharply to the east-north-east till it reaches the head of the 

 N'Debe, near Gobogobo trading station. Midway in this diagonal 

 course it is crossed by a branch of the Gap running east-south-east. 

 This branch, which afterwards becomes the principal Gap, dies out 

 on the surface, westwards, before it reaches the Gcua, its upward 

 intrusion having been apparently stopped by a thick sheet of 

 dolerite ; nevertheless at the crossing it has cracked the dolerite on 

 the under surface, and thin veins of the dioritic material have been 

 squeezed into the dolerite. The rock at the crossing of the twO' 

 branches forms a remarkable surface feature, owing to its weather- 

 ing out in immense blocks as large as the ordinary Kaffir houses. 

 Eastwards of the crossing, we have two Gaps, which soon turn back 

 to a due easterly trend and run parallel, separated by about half a. 

 mile of undisturbed Karroo sandstone and shales. 



In the following description we shall first follow the northern 

 branch, which is the continuation of the one that was found crossing 

 the Gcua River. It crosses the main road from Butterworth to 

 Kentani, a little north of the trading station of Gobogobo ; it is seen on 

 the ridge on which the road lies, in the form of isolated boulders of 

 the peculiar rock imbedded in the soil. On either side of the ridge 

 looking east and west one sees two long depressions, the one on the 

 west being the N'Debe River, that on the east containing a number of 

 streams all endeavouring to assume the prevailing south-east trend, 

 but being forced by the Gap to take, for a certain distance, an 

 easterly or westerly course ; each streamlet is separated from the 

 next by a low nek. In this way the Gap reaches the Kobonqaba 

 River, where it apparently stops, no evidence of the rock being found 

 in the river-bed ; but to the east we find, not a gap, but a ridge» 

 whose summit runs due east and west and is composed of a par- 

 ticularly micaceous variety of the Gap-rock ; this outcrop is only about 



