350 SALTPETRE KOP 



Saltpetre Kop is a very prominent hill in the Suther- 

 land Division, rising about 1,000 feet above the general 

 level of the high plateau on which it stands. It is com- 

 posed of breccia and tuff, filling a vent about 1,000 yards 

 long by 600 wide. The vent traverses the Beaufort beds 

 which are turned upwards for a considerable distance 

 on all sides ; the dip of the Beaufort beds is extremely 

 slight in the surrounding district, but at points about a 

 mile and a quarter from the neck the strata have a dis- 

 tinct dip away from it and the inclination increases as 

 the neck is approached, so that near the breccia the beds 

 are nearly vertical. 1 Bound about this large neck are 

 nineteen others of smaller size and forty-six dykes, mostly 

 filled with fine tuffs or breccias. In the case of one 

 dyke the rock has been found to be largely composed of 

 one of the less basic plagioclase felspars, and is evidently 

 an igneous rock of somewhat peculiar character, but it 

 has been greatly altered by the substitution of calcite, 

 hydrated ferric oxides, and silica for some of its original 

 components. The breccias and tuffs vary greatly, but 

 they all consist mainly of fragments of sedimentary 

 rocks set in a matrix of similar substances finely com- 

 minuted ; but in addition to these constituents there 

 are pieces of granite, gneiss, mica schist and Karroo 

 dolerite, and also mica, hornblende and ilmenite, identi- 

 cal in character with the similar minerals in the Silver 

 Dam breccia. Parts of the breccias and tuffs are 

 strongly impregnated with carbonates of lime and mag- 

 nesia, barium sulphate, hydrated oxides of iron and 



1 A fuller description and plans of the Saltpetre Kop area will be found 

 in O. C., viii., and T. P. S. S. A., vol. xv., p. 61. 



