32 VEINING OF SLATES BY GRANITE 



the first to record pinite, an alteration product of cor- 

 dierite, in the biotite-granite there. 



The contacts of the granite and clay-slate at Sea Point 

 and in the Platte Klip ravine have long attracted con- 

 siderable attention. 



On the beach at Sea Point the junction of the two 

 rocks is an extremely interesting one. First of all 

 some intrusions of very fine-grained granite are found 

 cutting across the tilted and much indurated dark 

 spotted slates. A short distance farther to the south- 

 west the latter are penetrated by such a network of 

 granite veins that an intimate mixture of slate and 

 granite, forming a belt approximately 100 yards wide, 

 lies between the spotted slates and the granite. A re- 

 markable feature is the coarsely porphyritic nature of 

 the granite in contact with the slates and in the narrow 

 veins that penetrate them. In many of the stripes of 

 slate the bedding planes are still recognisable, and their 

 junctions with the granite are sharp ; in others there is 

 a gradual transition from the sedimentary to the igneous 

 material, and grey streaky rocks have been produced in 

 which well-formed orthoclase crystals of ten-form " eyes ". 

 It is clear that under the influence of the molten granite 

 fragments of slate were softened or even melted, and 

 became partially incorporated in the invading magma ; 

 the whole character of the belt of mixed rock indicates 

 a drawing out of the composite mass while yet plastic. 

 Further west isolated streaks and fragments of slate 

 occur in the porphyritic granite. This zone of mixed 

 rocks can be traced from Sea Point to the foot of Table 

 Mountain. 



