478 GEOLOGY OF CAPE COLONY 



at Dordrecht a dolerite dyke cutting through a seam of 

 impure coal contains minute vesicles filled with mineral 

 oil. Again, in Barkly East oil and tarry matter are 

 found in joints in basalt at Bulhoek (Smiling Vale), 

 while at Moshesh's Ford small quantities of pitch occur 

 in crevices in the agglomerate filling a large volcanic 

 neck. The Molteno beds, containing occasional seams 

 of coal, underlie all this area, and the existence of these 

 small quantities of hydrocarbons is thus capable of 

 explanation. 



Salt. In Cape Colony all the salt produced commer- 

 cially is obtained from salt-pans. Such pans are nu- 

 merous in the north, but it is surprising that the pro- 

 duction of salt has been confined to so few of them, for 

 the product has a considerable commercial value and 

 the supply is practically unlimited. The salt-pans form 

 one of the most valuable assets of the Colony. 



As mentioned on page 412, most of these pans are 

 located upon the Dwyka tillite or shales namely, 

 Riverton, Klokfontein, and the Salt-pan (Herbert), 

 Zoutpan and Maritz Dam (Prieska), Zout Aar (Brits- 

 town), the Salt-pan, Eautenbach's Pan, possibly Matsi- 

 man Pan (Gordonia), and Commissioner's Salt-pan 

 (Calvinia), to mention a few of the important ones. 



Over the whole of Cape Colony water from the 

 Dwyka formation is frequently of a very brackish char- 

 acter, and the source of the salt in the pans is there- 

 fore obvious, the saline material having been gradually 

 leached out of the surrounding rocks and concentrated 

 in the depressions constituting the pans. 



