PRE-CAPE ROCKS OF THE NORTH OF THE COLONY 77 



with which quartz-porphyries of a peculiar type are 

 intercalated on Leeuw Draai. The lavas are basic 

 pyroxene-andesites with much devitrified glass ; usually 

 the larger crystals, both felspars and pyroxenes, are re- 

 placed by alteration products, of which epidote is the 

 most conspicuous. Augite and enstatite are present, 

 but the latter is always altered. A rather characteristic 

 feature of the lavas and also of the diabases along the 

 boundary faults, as seen under the microscope, is the 

 presence of magnetite crystals arranged in long strings 

 in the glassy base. The lavas are markedly amygda- 

 loidal ; the amygdales are of epidote or chalcedony, or 

 both together, and the bright green colour of the epidote 

 amygdales contrasts strongly with the red matrix, giving 

 a remarkable appearance to some of the lavas. 



Tuffs and breccias are interbedded with the flows. 



The intercalated quartz-porphyries are red rocks con- 

 taining corroded quartz and felspar crystals, also felspar 

 crystals with which quartz is intergrown ; small but 

 well-shaped crystals of a pyroxene have been replaced 

 by chlorite and epidote. The relation of these por- 

 phyries to the lavas is uncertain ; they may be inter- 

 calated flows or intrusions ; if they are intrusions they 

 reached their present position before the conglomerates 

 of the Koras series were formed, for the latter contain 

 pebbles of both amygdaloid and porphyry. 



The conglomerates, sandstones and quartzites of the 

 upper part of the Koras series are separated by an un- 

 conformity from the volcanic rocks. The pebbles in 

 the conglomerates are chiefly of quartzites and schists 



