476 GEOLOGY OF CAPE COLONY 



percolating water and collected in cracks and fissures 

 or brought to the surface. 



Veins of pyrolusite (manganese dioxide) have been 

 opened out on Constantia Neck, at Du Toit's Kloof 

 near the Paarl, at French Hoek and at Kogel Bay, 

 while a peculiar deposit is found at the Caledon Baths 

 which owes its origin to hot springs. The veins have 

 so far proved disappointing, the limited amount of ore 

 preventing their being worked on a large scale, otherwise 

 the ores appear to be of sufficiently high grade to justify 

 exploitation. The ore bodies tend to pinch out, and 

 much that at first sight appears to be solid ore proves 

 only to be a coating on the sandstone, and hence often 

 the ore is very low in grade. Judging from the history 

 of manganese mining in the Cape Colony a word of warn- 

 ing is sadly needed. 



The following two analyses of ores were made at the 

 Imperial Institute, London, the first sample having been 

 obtained from Constantia Neck, the second from Du 

 Toit's Kloof, Paarl : 



Manganese dioxide . . 83*93 7713 



Manganous oxide . . 5' 55 4 '04 



Ferric oxide . . . 2 '13 2 '23 



Silica 1-14 4'96 



Phosphoric oxide . . 0'61 0'75 



Sulphur .... nil nil 



Mica. White mica (muscovite) has been found in 

 pegmatite veins in granite in various parts of Cape 

 Colony, for example, Alicedale and Middel Water in 

 Prieska. It is only rarely the case that sheets can be 

 obtained exceeding a few inches in size, and almost in- 



