45 



50. We have incidentally referred to lime as one of the 

 food-materials which are only scantily provided in average 

 Cape soils. Of course there are places where the subsoil is 

 calcareous, but these are few and far between. In the 

 Karoo, deposits of lime are local, and apparently scattered 

 about capriciously over that great area, it may be as well 

 to observe that these incidental deposits have a curious and 

 peculiar origin. They are clearly what mineralogists term 

 kalk-sinter. When the Karoo in geological times was a 

 great fresh-water lake, where the Dicynodon wallowed 

 amid the mud and rushes, much as the hippopotamus does 

 in Central African lakes this day, there were hundreds of 

 places where springs rose up at the bottom underneath the 

 sheet of water. These deep-seated springs were very largely 

 charged with lime ; in fact, they might have been called 

 lime-water springs coming from calcareous strata lying at 

 great depths. When their water reached the exit of the 

 fissure at the bottom of the lake and diffused itself through 

 the liquid mass, much of the carbonic acid gas, by the aid 

 of which the lime had been kept in solution, was lost by 

 diffusion. The natural result was deposition of a precipi- 

 tate of lime all round the mouth of the fissure, making a 

 sort of calcareous floor, extending perhaps for many yards 

 in every direction, with the eye of the spring as a centre. 

 This process of deposit would go on just so long as the 

 fissure was open for the exit of the water. But in course 

 of time the same causes that produced the deposit on the 

 lake floor would cause a similar precipitation in the upper 

 part of the fissure delivering the spring, and would ulti- 

 mately choke it altogether. After that there would be an 

 end to any further lime deposit in that place. One can 

 easily understand this process going on at the bottom of 

 the lake, when examining pipes which have carried a stream 

 of calcareous water for many years and show their original 

 calibre reduced by deposit inside to one half or even less. 

 After the great upheaval of the claystorie porphyry just 

 south of the Karoo lake, numerous huge cracks were made 

 on the southern edge of the Karoo basin. The water of the 

 lake was drained off down the lines which we now recog- 

 nize as the kloofs and passes of the Zwartberg, Langeberg 

 and its other boundaries. The farmers of the Karoo are 



