THE KARROO SYSTEM 177 



another during the folding of the rocks, that in the 

 absence of favourable exposures it is impossible to be 

 certain of the glacial origin of the scratches immediately 

 below the boulder-bed. 



At Eland's Vlei, near the confluence of the Tanqua 

 and Doom (Clanwilliam) Eivers there is exposed a 

 " striated pa'vement " not of the underlying rock, but of 

 the tillite itself, which passes under a further thickness 

 of boulder-bearing material. The pavement is a flat 

 surface of tillite in which there are numerous boulders 

 up to three feet in diameter pressed down flush with the 

 surface of the pavement. These boulders are finely 

 striated in a direction which is almost due east ; such 

 striae as they may have running in other directions 

 have been largely obliterated by the agency which pro- 

 duced those mentioned. The matrix of the tillite, a 

 tough blue sandy mudstone, is traversed by numerous 

 furrows running parallel to the dominant striae on the 

 boulders. There can be little doubt that this surface, 

 which is from fifty to eighty feet above the base of 

 the boulder-bed, was produced by ice moving across it. 

 After the ploughing up of the. glacial material the ice 

 disappeared and a sandy mud with boulders and pebbles, 

 precisely like the tillite below, was deposited upon the 

 "pavement ". 



A similar example has been found in the Vaal Eiver 

 Valley a few miles north-west of Kiverton, the direction 

 of the striation and furrows being from north-east to 

 south-west. Many instances o| such surfaces occur in 

 recently glaciated regions ; they are produced whenever 



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