TUli FAULT S^■STI•:.\IS IN SOL'TIl i )F S(»L"TH AFRICA. y^J 



The Cango fault in ( )udtshoorn is a direct east and west 

 tank under tlie Zwartherg MuuPitains. To understand the 

 somewhat comphcated relationshi]) hetween the folds of the 

 Zwartherg and the fault, we can have recourse to a homely 

 illustration. The southern fold of the Zwartherg is an anti- 

 cline ])iTching to the ^vest near Calitzdorij, and pitching to the 

 east near Meirin.g's Poort. .^uch a fold ma\' be rejjresented by 

 an U]iturncd lioat. Imagine the boat to be full of sand now 

 forming a mound covered l)y the l)oat. On the south side, half- 

 wa\- between the keel and the outer edge, make a longitudinal 

 cut and drop the outer portion ; this cut represents the Cango 

 fault. Now ctit away all the central ])oi-tion of the keel between 

 the bows and the stern. The underlxing sand will appear; 

 scoop a large quantity of this away, and the boarding of the 

 boat still remaining will consist of the bows and the stern united 

 0*1 the north side by what is left of the side of the boat. This 

 boarding represents the Table Mountain sandstone of the 

 Zwartherg, and the sand re]:)resents the underlying Mahiiesbury 

 l)eds of the Cango. Actttally the line of the fatilt is covered 

 b} cretaceotis deposits, for the Cango fault, after slicing oil the 

 older rock's in the manner just indicated, became a line of renewed 

 movement, this time bringing down the cretaceous beds with it. 

 Suess has called a fold that is developed on the lines of a pre- 

 vious fold which has died out a posthumous fold. I do not 

 think, however, the term [JOsthumous is suitable for the case of 

 a fault develojiing on the line of an old fracttire. but the recog- 

 nition that a fault-])lane can be the seat of two movements 

 scjiarated b\' consideralile periods of time is not always borne 

 in nn'nd. The want of it has led to con.siderable confusion, 

 especialb' al')ng the W'orcester-Swellendam fault, where the same 

 renewed movement took i)lace in the cretaceous fault-])it lying 

 to the east of the town of Robertson. 



The faults of the X^.S. line of mountain'^ are not of an\'- 

 thhig like the importance of those in the K.W. direction. The 

 faults occur, but while they throw the ground in the sense of 

 the imbricate structttre, since they only bring up Bokkeveld beds 

 against Table ]\Iotintain sandstone, the}' can be looked on as 

 or(linar^• accompaniments of folds. 



The Trough System of Faults. 



Supposing one had a wheel with some square ])egs let into 

 the rim. and this wheel were run over some soft substance like 

 clay or dough, the pegs wottld make dents at intervals, separated 

 by undisturbed clay or dough. The dents would he in a definite 

 line, and would belong to the same series. So the fault-pits of 

 this system of fractures, although they are separated by tindis- 

 turbed tracts of cotintry, may be said to belong to certain linear 

 series. The wheel has rttn in three parallel courses over the 

 coa-tal districts of Cape Colony, and there are consequently 



