178 LOWER DWYKA SHALES 



a glacier or large sheet of ice moves over a floor of 

 boulder-clay or till. 



A short distance north of Karroo Poort shales make 

 their appearance between the tillite and the quartzites 

 of the Witteberg series ; southwards and eastwards they 

 rapidly become thicker. They consist of greenish and 

 bluish shales and thin quartzitic sandstones and are in 

 all from 400 to 1,400 feet thick, measured from the 

 uppermost thick quartzite of the Witteberg group to the 

 lowest bed that is distinctly pebbly. Some of the strata 

 are very like the shales of the Witteberg, and others, 

 especially near the top, are of the same nature as the 

 matrix of the tillite. Although they are undoubtedly 

 passage beds between the two formations, they are 

 placed for convenience with the boulder-beds and are 

 called the Lower Dwyka shales. On the Witteberg 

 Eiver the shales have been found to contain impressions 

 like the Phyllotheca stems of the Ecca beds ; fossil stems 

 have also been found in the Lower shales near Zoe- 

 tendal's Vlei in Willowmore. 1 



The Lower Dwyka shales are well exposed at many 

 places along the north flank of the hills formed by the 

 Witteberg series along the Southern Karroo, e.g., near 

 Matjesfontein, in the Witteberg's Eiver south of Laings- 

 burg, at the north end of the Buffel's Eiver Poort (Leeuw 

 Kloof Poort), south of Prince Albert, and in Willowmore. 

 In the neighbourhood of Kando's Poort and at Zoeten- 

 dal's Vlei the Lower shales are over 1,350 feet thick. 

 At Graham stown, both to the north and south of the 

 town, similar shales 650 feet thick intervene between 



1 Schwarz, O. C.,viii., p. 94. 



