418 HOT SPRINGS 



hot springs has a similar source is of course not 

 known. 



At Tarka Bridge l near Cradock saline water at a tem- 

 perature of about 80 F. issues from four bore-holes. 

 The most remarkable feature about them is the fact 

 that the water rises and falls at twelve and a half hour 

 intervals in a manner analogous to the oceanic tide. 

 The bore-holes clearly draw their supplies from the same 

 underground source, for the composition and tempera- 

 ture of the water is the same in each case, while the 

 pumping of one hole affects the discharge from the 

 others. 



The probable reason of the high temperature of the 

 springs is that the water comes from great depths. So 

 far as one can judge from the surface geology none of 

 the springs is in any way connected with volcanic ac- 

 tion. Many of the older travellers took the dark slaggy- 

 looking deposits of hydrated ferric oxide at Caledon for 

 lava, but the dark rock is derived from the ferrous car- 

 bonate in the water by oxidation on contact with the 

 air. In the Western Karroo there are several cold springs 

 at the foot of the Zwart Kuggens that leave a similar 

 deposit of limonite, but there is hardly sufficient iron in 

 the water to make it taste unpleasant. 



1 Young, A., Papers read at the joint meeting of the Brit, and 

 S. A. A. A. S. in 1905, vol. ii., p. 144. 



