480 GEOLOGY OF CAPE COLONY 



At the north-west extremity of the Tygerberg veins 

 of quartz carrying cassiterite occur, apparently in 

 the Malmesbury beds. Several other localities are 

 known at which small amounts of tin have been 

 proved. 



The origin of the cassiterite is evidently closely 

 connected with the granite intrusions of the Western 

 Province, and the junctions of the igneous rock with the 

 slates are worthy of more attention than has yet been 

 paid them, while in addition the possibility of important 

 deposits of alluvial tin in the low ground in this area 

 should be borne in mind. 



The granites in the Western Province contain a good 

 deal of tourmaline in places, but the presence of that 

 mineral, however, must not be regarded as an important 

 indicator of the existence of cassiterite. Of the other 

 minerals which usually accompany tin ore in various 

 parts of the world, wolfram has been found at Kuil's 

 Kiver and molybdenite in the Helderberg granite along 

 with mispickel, but neither topaz, monazite, nor beryl 

 have yet been recorded. 



Water. The finding of underground water which will 

 either rise to the surface through a bore-hole, or which 

 is within a practicable distance for pumping, is a very 

 important question in the inland and north-western 

 districts. In the folded belt there are permanent streams 

 in the mountains and springs are fairly numerous, but 

 in the interior the majority of farmers are dependent 

 on wells or bore-holes. There are no rocks in the in- 

 terior of the Colony of such loose texture that they form 



