402 INLAND LIMESTONES 



compact, and it contains numerous sand grains and 

 other particles derived from the soil. The calcareous 

 matter collects together in certain spots and forms irre- 

 gularly shaped lenticular lumps ; neighbouring masses 

 coalesce and produce layers. The bulk of the clayey 

 material in the soil seems to be pushed aside by the 

 calcite, but the sand grains remain behind. This rock 

 is well shown in some of the railway cuttings between 

 Heidelberg and Eiversdale. It is similar to the " Kan- 

 kar " of India. 



In Northern Cape Colony thick calcareous deposits 

 have formed in a similar manner below a covering of 

 red sand. 1 Some of the calcareous tufas in the Orange 

 Kiver Valley, as in the neighbourhood of Hopetown, 

 have been formed on terraces cut by rivers in former 

 times. 



The springs that come from the Bokkeveld series and 

 from the Karroo beds frequently deposit a white tuface- 

 ous limestone which forms irregular layers in their 

 neighbourhood, filling up the joints of the exposed 

 rocks and cementing together the particles of soil. At 

 the foot of the escarpment of the Kaap Plateau there is 

 a great development of tufaceous limestone deposited 

 through the agency of springs. 



The sediments of the Karroo formation contain a fair 

 proportion of carbonate of lime, and the dolerite which 

 is so abundant in the form of intrusions in these beds 

 contains about 10 per cent, of calcium oxide ; this, on 

 the decomposition of the dolerite, is chiefly converted 

 into carbonate of lime. From these two sources the im- 

 1 O. C., xi., p. 126. 



