PRE-CAPE ROCKS OF THE NORTH OF THE COLONY 97 



the crystalline limestones are not like those of the 

 Campbell Kand series nor are the cherts similar to those 

 of the latter. A curious feature in the Griqua Town 

 tillite is the occurrence of numerous nodules of chert 

 unlike any that have yet been found in situ in South 

 Africa. That these nodules are pebbles in the tillite and 

 were not formed in it is proved by their having been 

 scratched like other boulders and also by their manner 

 of occurrence. The absence, so far as yet known, of 

 boulders of granite, etc., is a very remarkable fact. 



In its least altered state the rock has a blue or grey 

 colour, but in many places it is red or brown owing to 

 the presence of hydrated ferric oxides. Where the rock 

 is red the limestone pebbles have been dissolved away, 

 and their room is partly filled by specular iron ore. 



The tillite is under 100 feet in thickness at the most, 

 usually less. It is apparently thickest on the farm Punt 

 in the Hay Division, but the rock is not frequently well 

 exposed for measurement. Near Koegas it is only 

 about ten fest thick. It has been found at many places 

 between Madebing in Bechuanaland and the Orange 

 Eiver, and the area in which the known outcrops occur 

 is some 8,000 square miles. It does not often make con- 

 spicuous outcrops, but where the Ongeluk beds form a 

 prominent escarpment the tillite is often found at or near 

 the base of it ; otherwise the tillite is usually concealed 

 by soil. 



Above the tillite there may be a thickness of thirty 

 feet of shales and jaspers between it and the lavas of the 

 Ongeluk beds, but along the Kuruman River, near Upper 

 Dikgathlon, the lavas follow the tillite directly, and the 



