THE KARROO SYSTEM 187 



as yet only known in place in the north of the Colony. 

 In the Tanqua Karroo quartzites and sandstones of 

 various kinds predominate ; some may have come from 

 the Table Mountain and Bokkeveld series north of the 

 unconformity. Along the west and south of the Karroo 

 the boulder-bed contains numerous inclusions of micro- 

 cline-granites like those of Northern Cape Colony, quartz- 

 ites and quartz-schists from the Kheis series, diabase 

 and amygdaloids like those of the Ventersdorp system, 

 cherts, limestones, and dolomites from the Campbell 

 Kand series, banded jaspers and ironstones from the 

 Griqua Town series, and purple quartzites, grits, and 

 conglomerates from the Matsap beds. 



The bulk of the formations that have supplied the 

 boulders of recognisable origin are only known in the 

 north ; there is no clear evidence that any of them had 

 a southern origin, and so far as is known the Dwyka 

 was laid down conformably to the Cape formation 

 throughout the south of the Colony. 



The boulder-beds are about 1,000 feet thick in the 

 south of the Karroo, but the thickness diminishes 

 northwards. Where it lies nearly horizontally, as in the 

 north of the Colony, it covers wide stretches of country, 

 but is of varying thickness though never more than 

 a few hundred feet. 



In Griqualand West the tillite was deposited upon a 

 very uneven surface, and the variation in level of the 

 old floor is often very considerable ; a change of altitude 

 of as much, as 800 feet is known to occur within a dis- 

 tance of a few miles. The glacial deposits are in conse- 

 quence much thicker in the depressions than over the 



