686 ERNEST H. L. SCHWARZ 



The full conformable series is found only on the south; on the 

 north, the series begins with the Dwyka Conglomerate, here a sub- 

 aerial deposit, which can be followed southward along the rim of the 

 structural basin to where it is essentially a subaqueous deposit, and 

 the Witteberg, Bokkeveld, and Table Mountain beds may be seen 

 coming in successively beneath it. The Stormberg beds, again, are 

 only found in the east. 



The Griquatown beds are a highly ferruginous series of shales 

 and slates, sometimes moderately soft and unaltered, when the 

 characteristic color of the whole is blue-black, and the fissures are 

 filled in with blue asbestos or crocidolite. But more often an intense 

 alteration has taken place, and the rocks have become jaspers and 

 quartzites, heavily charged with hematite and magnetite, and the 

 crocidolite has been changed to the quartz pseudomorph, the beau- 

 tiful honey-yellow tiger eye. Near the top of the series, in the dis- 

 trict of Hay, west of Kimberley, there is the well-developed glacial 

 till, the matrix now converted into a red jasper; yet the bowlders 

 of chert, when weathered out, show the unmistakable faceting and 

 scratching which can have been caused only by glacial action. 

 The freshness of the appearance of the ice-scratched bowlders is 

 the more remarkable when one reahzes that not only the matrix, but 

 the inclusions as well, have been indurated by metamorphism. 

 The size of the bowlders varies up to two feet, and they are scattered 

 at random through the matrix, to which they bear a very small pro- 

 portion in regard to bulk; but occasionally there is a small bed of 

 pebbles or coarse grit. Mr. Rogers records at one locality a number 

 of " Dreikanters, " but I do not know whether anything additional 

 can be learned from them. I have found them in large numbers in 

 some of the Witwatersrand conglomerates. The whole thickness 

 of the glacial till is probably under loo feet, but the extent of country 

 covered by it in the area already mapped is over i,ooo square miles. 



The Table Mountain sandstone glacial bed is very similar in 

 position and character, though not of course in metamorphism, to 

 the Griquatown one. When the Geological Survey commenced 

 operations, there were two series of quartzites, the Table Mountain 

 and the Witteberg, which had been mixed up, so that, in order to 

 find some way of either distinguishing or definitely joining up the 



