3/0 THE FAULT SYSTEMS IX SOUTH UF SOUTH AFRICA. 



alsu hoped that this dent would gradually heal itself by the 

 forces acting" on the plastic medium due to the rapid revolution. 

 In the case of the earth, had such a meteorite fallen, then the 

 dent would have been a seething cauldron of molten rock due 

 to the heat caused by the impact. This would crust over by 

 dissipation of heat into space, and a region of tremendous volcan- 

 ism would result, such as we know existed in the North Atlantic 

 between the north of Ireland and Iceland, extending to Green- 

 land. It is, however, not within the scope of the present ])aper 

 to follow out this particular line of reasoning. I have men- 

 tioned the experiment to show how possibly faults may precede 

 folds, although this fact is not yet established by direct observa- 

 tion. 



In regard to space, faults, generally speaking, are deep- 

 seated, and folds are superficial. In crossing folds and faults 

 the fold would ride over the fault. There are no good in- 

 stances in this country, but what is meant can be illustrated by 

 the rift valley in which the upper Rhine Valley lies. The great 

 fault-trough of the Red Sea is followed, after an interruption 

 in the Sinai region and in the Mediterranean, where surface 

 features are hidden by the water, by the fault-trough of the 

 Adriatic. North of this there is the great barrier of the Alps, 

 and vet to tlie north the fault-trough, much diminished it is 

 tRic, appears along the Rhine. The fault-trough has dived, 

 as it were, beneath the Alps. Another branch of the Red Sea 

 trough, which runs up the (lull of Akaba, forms the walls of 

 the Dead Sea and the Valley of the Jordan, and ends at Lake 

 Tiberias. Here there are the feeble outposts of the fold-system 

 of Eurasia, which have proved sufficient to stop the further pro- 

 gress of the fault. In this latter case, then, the earth-crack 

 has not been sufficiently powerful to overcome the barrier of 

 the fold. 



So much for the bearing of faults on the country through 

 which thev pass. In regard to the details exhibited by faults. 

 we have many very excellent and characteristic types in S(<uth 

 Africa. In typical' fauks the break is a clean-cut fracture; one 

 side sinks down, the other remains stationary. Such faults 

 may be exemplified by the great Worcester-Swellendam fault. 

 The rocks there were unable to stand the tension, and simply 

 parted. No signs of friction along the fault plane are noticeable. 

 This would have happened had there been any pressure of the 

 one side against the other while the movement was in progress ; 

 or if the side that was sinking, instead of doing it vertically, 

 became tilted forwards b}- the hinge-like movement of the strip 

 of ground on the counter side of the fault. On the other hand, 

 there was not an excess of tension causing a gap between the 

 two sides of the fault. Occasionally one comes across, in South 

 Africa, a fault with an ojiening between |he two sides ; such^ a 

 case occurs in the di^^trict of ^latatiele, where a dyke of dolerite 

 is inserted along the plane of the fault. Underground faults are 



