INTRODUCTION 8 



In the eastern part of the Colony, beyond the Gualana 

 River where the southern mountainous region is cut 

 through by the coast, the descent from the watershed 

 to the coast is more uniform than in the west ; it is 

 unbroken by mountain ranges, but is more of the na- 

 ture of a succession of terraces than a gradual slope. 

 There is thus no area in the east corresponding to the 

 Great Karroo of the west and midlands. 



Before describing the geological structure of the 

 Colony, it will be convenient to give a general account 

 of the various groups of rocks that built it up. The 

 classification of these rocks, which will be used in this 

 book, is on pages 4 and 5. 



The Pre-Cape rocks are a heterogeneous collection of 

 sediments and igneous rocks both extrusive and intrusive. 

 The sediments can be divided into two great groups, 

 those older than the intrusions of granite and those 

 which were laid down subsequently to the intrusion. 

 It is unfortunately not known whether there was more 

 than one period during which intrusion of granite took 

 place, but it is possible that the Bechuanaland granite 

 is older than that of Prieska and Upington. The later 

 sedimentary rocks were folded and subjected to pro- 

 longed denudation prior to the deposition of the Cape 

 system. 



Beyond the statement that all these rocks are older 

 than the Devonian (lower half of the Cape system) 

 nothing can be said as to their age, but they must re- 

 present an enormous lapse of time. 



The Cape system is a group of sandstones, quartz- 

 ites and shales some 10,000 feet thick lying unconform- 



