80 Transactions of the Boyal Society of South Africa. 
ontcrops make slight rises on the floor, probably never more than 6 inches 
high. 
The most remarkable fact about the floor, after its flatness, is the 
thinness of the layer of sandy mud. The total area of bare shale and 
limestone surface within the pan must be considerable, and over a still 
wider area the joints traversing the rocks below are clearly outlined by 
damp streaks or lines of salt left behind on the evaporation of the water 
along the joints. This indicates that the mud covering the shale is thin. 
At several places I scratched away the mud and exposed shale at a depth 
less than 4 inches. The mud contains small crystals of gypsum. In an 
abandoned well or prospecting pit in the middle of the eastern part of the 
pan there is exposed a section showing 3 inches of sandy mud lying on 
a quarter of an inch of gypsum, directly below which are dark shales with 
occasional thin layers of fibrous limestone. 
Though there is much mud where the Olifant's Vlei Eiver comes into 
the pan, and at the time of my visit in September, 1909, this mud was 
still so soft that I could not cross it, there seems to be no buried channel 
in the pan itself, and the silted-up bed of the Olifant's Ylei Eiver cannot 
be much deeper than the level of the dolerite lip, over which part of its 
waters are discharged. 
There can be no doubt that the pan is essentially a flat surface cut in 
the shales. The presence of the hard dolerite lip checks the downward 
cutting of water in the shales behind it. The shales, though some layers 
are hard, are fragile rocks which break up into small fragments on 
exposure ; the limestones are more resistant rocks, but owing to their 
nbrous structure they break up much more quickly than the calcareous 
layers and nodules in the Dwyka tillite. 
There was no vegetation on the mud of the pan in September, 1909, 
but the shale patches bore clumps of a small-leaved, bright green, succulent 
plant, especially towards the outer part of the pan. Though there were 
no visible deposits of salt beyond occasional films a few feet wide, and the 
lines marking joints in the underlying shales, the sandy mud of the floor 
probably contains a fair amount of common salt in addition to the small 
gypsum crystals scattered through it. 
The Upper Dwyka shales yield brackish water, but in September of 
last year water in the long kolk in the course of the ill-defined valley 
leading from the east side of Bushman's Berg was still fresh enough to 
drink, though that in the pools along the Olifant's Vlei Eiver was useless 
to man and donkeys. Water flowing westwards from the latter river over 
Yerneuk Pan must bring salt with it, some of which remains behind on 
each occasion. 
The explanation of the cutting of such a wide tract of flat country as 
Yerneuk Pan is not easy to find, but a consideration of the behaviour of 
