398 Transactions of tJie SoutJi African Philosojjhical Society. 



the lead moved as a liquid, that between the two surfaces w^as forced 

 to flow outwards only, and hence carried with it the portion of pencil 

 embedded in it. 



The pebbles of limestone seem to have been pressed to just about 

 their crushing strength, for some are slightly cracked while others are 

 intact. The pressure is 6'72 tons, or say 15,000 lbs. per square inch, 

 a value which agrees with the average given for American limestones 

 by Buckley." The extraordinary thing about these pebbles is that 

 the cracks are not at right angles to the direction of pressure, but to 

 the sides of the containing box. This I think indicates that there 

 must have been a balancing between the direction of crushing and 

 the sides of the vessel holding the lead ; at one time the sides w^ould 

 give way and the ram advanced ; at others, the sides were sufficiently 

 strong to prevent the ram moving. If now the operation had been 

 stopped w^hen the latter conditions were prevailing, the pressure 

 on the contained pebbles would have been normal to the sides of the 

 vessels, and the cleavage consequently parallel to them. The release 

 of pressure also probably allow^ed a slight vertical movement in the 

 lead, due to the elasticity of the sides, and in fact the needle of the 

 gauge went up to 80 tons and then came back to 75 tons. 



The experiment, however, proves that a pressure of 15,000 lbs. per 

 square inch is insufficient to keep the parts of a bit of hmestone 

 in contact when there is differential movement in the mass. 

 Whereas we have seen that when sufficient time is allowed the 

 ordinary atmospheric pressure is sufficient to effect quite large 

 deformations. 



I will now take the case of the pebbles distorted by Nature where 

 the element of time has had ample opportunity of coming into play. 

 The first is one from the Enon Conglomerate. I gathered the speci- 

 men (fig. 1, pi. V.) from a large quantity of similar ores occurring in a 

 high bank of red Enon Conglomerate, near Nuy Siding, on the 

 Worcester- Swellendam line. Most of the pebbles were too large to 

 carry away. The rock of which they are composed is a hard, sandy 

 mudstone, derived from the Ecca Beds of the neighbourhood. It 

 will be noticed that this has been crushed and deformed as if it had 

 been simply a mass of plastic clay. There is no question of the 

 pebbles having been soft at the time of squeezing ; we have the rock 

 from which they are derived within a short distance of the Enon 

 Conglomerate, and in both the physical state of the sandstone is the 

 same. There is no question also of water having played a part 

 in the moulding of the rock, for the cracks quite open, and there are 

 no infiltration products like in that figured by W. S. Gresley, from 



* "Building and Ornamental Stones," Madison, 1898. 



