Vol. 67.] WORCESTER, ROBERTSON", AND ASHTON (CAPE COLONY). 731 



temporaneous with the formation of the Enon Conglomerate, but it 

 was certainly for the most part later than the formation of this 

 deposit. 



One more point still remains to he dealt with, that is to say, the 

 extent of the Worcester Eault. Many estimates have been given 

 of the maximum throw of this fault as at present existing, and it is 

 undoubtedly very great. At its most favourable development it 

 brings into contact Enon Conglomerate and Malmesbury Slate, but 

 the throw is not necessarily represented by the thickness of all the 

 strata which elsewhere occur between these limits. At different 

 points the conglomerate rests upon Ecca, Witteberg, and Bokkeveld 

 Beds ; and, as we have seen, there is reason to believe that before the 

 formation of the fault these rocks had undergone very considerable 

 folding and denudation, so that it is obviously incorrect to add 

 together the total thickness of the missing formations to obtain the 

 throw. We can only say with absolute certainty that the throw 

 must be at least equal to the difference of level of the upper surface 

 of the Malmesbury rocks on either side of the fault, and there is 

 unfortunately no means of measuring this directly. The lowest bed 

 on which Enon Conglomerate rests directly is the Bokkeveld, so the 

 minimum throw must be at least equal to the sum of the thicknesses 

 of the Table Mountain Sandstone and part of the Bokkeveld, but 

 this need not necessarily be much more than 5000 feet. This may 

 be regarded as the lower limit. On the other hand, the higher limit 

 is, as explained above, the total thickness of all the strata between 

 the Malmesbury Series and some horizon in the Ecca Series. 



The thicknesses may, then, be tabulated as follows : — 



Feet. 



Ecca Sandstone 1000 



D wyka Conglomerate 2000 



Witteberg Series 2500 



Bokkeveld Series 2500 



Table Mountain Sandstone 5000 



Total 13,000 



It is here assumed that the highest Ecca bed seen along the 

 fault is 1000 feet above the top of the Dwyka, and this, although 

 a very rough estimate, is probably not far from the truth. 



Hence we see that the throw of the fault must be something 

 between 5000 and 13,000 feet, and in all probability it is nearer to 

 the larger figure than to the smaller. It is of course possible, and 

 indeed highly probable, that the throw of the fault varies, since it 

 has a visible length of some 70 miles and may be continued much 

 farther. At any rate, it may safely be said that in the middle of 

 its length, near Robertson, the throw is probably something like 

 10,000 feet, and perhaps more, a figure which is certainly large 

 enough to justify its inclusion among the greatest dislocations at 

 present known to geological science. 



Q.J. G. S. No. 268. 3d 



