Vol. 67.] WORCESTER, ROBERTSON, AND ASHTON (CAPE COLONr). 7*27 



approximately at right angles. It is also noticeable that the fault is 

 curved, running nearly parallel at either end to each of the sets of 

 folds, and changing its general direction from north and south at 

 one end to east and west at the other. From these considerations, 

 it is evident that the fault has a close genetic connexion with the 

 folding. 



Although these two phenomena are obviously connected, it must 

 not be assumed that they are contemporaneous : in fact, such is 

 clearly not the case. From a study of the structure of the rocks 

 of the Cape System on either side of the Worcester Fault, there 

 can be little doubt that the faulting is in the main later than the 

 folding, although it is probable from other considerations that no 

 long interval of time separated them. 



The faulting is certainly later than the rocks of the Ecca Series, 

 since the Dwyka Conglomerate and Ecca Sandstone and Shale are 

 brought into contact with Malmesbury and Cape rocks. The question 

 next arises, whether the fault is or is not newer than the Enon 

 Conglomerate; and to this it is somewhat more difficult to give a 

 conclusive reply, since some of the evidence is not very clear. The 

 most important fact to determine for this purpose is whether or not 

 the Enon Conglomerate is cut by the fault, and as to this some 

 doubt has hitherto existed. There is no doubt that the fault forms, 

 in a general way, the northern boundary of the Enon facies of the 

 Cretaceous in this region T ; but, on the maps of the Cape Geolo- 

 gical Commission, the conglomerate is mapped in places as just 

 overlapping the fault, apparently for a few hundred yards. This, 

 on the face of it, is improbable : if the present distribution of the 

 conglomerate is independent of the fault, it is unlikely that its 

 boundary would follow so closely the line of the fault for scores of 

 miles, and overlap it occasionally for a few yards only. There is 

 no real field-evidence for this interpretation, and the general form 

 of the patches of Enon Conglomerate is very strong presumptive 

 evidence in favour of their truncation on the northern side by the 

 fault, exactly in the same way as the Karroo rocks are truncated. 

 Hence, we may conclude almost with certainty that the Wor- 

 cester-Swellendam Fault is, at any rate in part, newer 

 than the Lower Cretaceous. 



Another line of argument may also be pursued, namely, that 

 derived from the character of the blocks and pebbles of which the 

 Enon Conglomerate is composed. In the first place, so far as my 

 own most careful observations go, the Enon Conglomerate at 

 Worcester, Robertson, and Ashton does not contain pebbles of the 

 Malmesbury rocks. The only possible exception to this is the 

 somewhat doubtful case described by Prof. Schwarz at Lange Kloof 

 near the Hex-River Pass, and as to this I am frankly sceptical, 



1 Dr. Rogers & Mr. Du Toit consider that the Enon Beds of the Oudts- 

 hoorn region were formed in a different basin of deposition ; see their 

 Gvology of Cape Colony ' 2nd ed. (1909) p. 321. 



