112 THE ZWART MODDER BEDS 



shales. That they were formed under shallow water 

 conditions is proved by the frequence of false-bedding, 

 ripple marks, and clay pellets in the arenaceous rocks. 



The only locality where the Zwart Modder beds have 

 been found dipping at fairly high angles is the neigh- 

 bourhood of Sannah's Poort, where an anticlinal fold 

 trends south 35 west. 



The exposed thickness of these beds is not less than 

 1,600 feet, and the total thickness probably exceeds that 

 figure considerably. 



At present the correlation of the Zwart Modder beds 

 with other formations in the north or south is impossible. 

 Resemblances to other arenaceous formations can of 

 course be seen in them, but for all that is known they may 

 with equal probability be assigned to any formation 

 younger than the Malmesbury and Kheis beds and older 

 than the Dwyka. 



MISCELLANEOUS INTRUSIONS OF THE NORTH. 



In the Pre-Cape rocks of the north there are many 

 igneous intrusions, chiefly dykes, which possess various 

 petrological characters. Their exact age is uncertain, 

 but that they are Pre-Karroo is indicated either by their 

 petrological character or by the fact that they pass below 

 and do not penetrate the Dwyka tillite. 



In the southern part of Prieska Poort in the Doorn- 

 berg the Griqua Town beds are penetrated by a small 

 boss or plug of pink syenite. Syenitic dykes, probably 

 of the same age as this intrusion, are found in the 

 western hills of the Doornberg. 



Near Klip Fontein in Hay there is a dyke of quartz- 



