EXPLANATION OF PLATES 449 



• Plate 50. — Dwyka Tillite and Witteberg Notch 



Figure 1. — A weathered slope of Dwyka tillite, near Matjesfontein. 



The sheet of tillite slopes to the left and weathers in spiked 

 outcrops on a faintly developed sehistosity transverse to the 

 sheet. In the distance, the west end of a synclinal ridge of 

 overlying Ecca sandstones (see page 403). 



Figure 2. — One side of the poort, or notch, of Witteberg river, southwest of 

 Laingsburg. 

 The notch is in a nearly vertical sheet of Dwyka tillite, looking 

 east. The attitude of the sheet is indicated by a layer of 

 conglomerate included in it, near the left margin of the view, 

 as well as by the attitude of bedded shales in the adjoining 

 valley. The transverse sehistosity is here well displayed by 

 weathering (see page 404). 



Plate 51. — Dwyka Shales and Dwyka Tillite 



Figure 1. — Vertical Dwyka shales. 



The shales are included between heavy sheets of tillite south- 

 west of Laingsburg, looking eastward. The white blocks are 

 fragments of Witteberg quartzite from the terrace or planation 

 surface which here truncates the vertical Dwyka (see plate 

 48, figure 2, and page 405). 



Figure 2. — Characteristic exposure of Dwyka tillite. 



The exposure is in a ravine north of Ngotsche, Vryheit, Natal 

 (see page 407). 



Plate 52. — Eroded Valleys and Ridges and glaciated Boulder 



Figure 1.— Ridges and valleys eroded on nearly vertical sheets of Dwyka tillite 

 and shales. 

 The view is southwest of Laingsburg, looking west-northwest. 

 The valley on the left is eroded on the basal shales ; the valley 

 on the right follows a weaker belt of tillite between two 

 harder belts. The continuity of these structural features 

 may be inferred from the continuance into the distance of the 

 features of relief dependent on them. The poort, or notch 

 (shown in plate 50, figure 2) is cut through the middle ridge 

 of this view where the road from the southern valley passes 

 through to the northern valley (see pages 397 and 404). 



Figure 2. — A glaciated boulder of Barberton slate. 



The boulder is in a ravine north of Ngotsche. Vryheit. The 

 hammer handle is half a meter long (see page 408). 



XXXIX — Bull. Geol. Soc. Am., Vol. IT, 1905 



