428 MR. W. GIBSON OX THE GEOLOGY OF THE GOLD-BBAHING 



4. Summary of Observations and Conclusions respecting the Physical 

 Helationships of the Gold-bearing Conglomerates and Associated 

 RocJcs. 



The facts brought forward in the foregoing account of the more 

 important sections within the limits of the typical Witwatersrandt 

 district seem to the writer to show conclusively (a) that the 

 Witwatersrandt strata have been subjected to great lateral pressure 

 acting from south to north ; that (6) they have been locally dislo- 

 cated, and the dislocated masses have been driven forward over each 

 other along more or less oblique thrust-planes. The crust-move- 

 ments have not only induced overfolding and overthrusting to such an 

 extent as in many cases to considerably alter the original relation- 

 ship of the beds, but have frequently changed, almost completely, the 

 original petrological character of the rocks. 



It has not been possible, with such knowledge as the writer has 

 been able to obtain, to determine with certainty the true geological 

 succession of the beds of the district as a whole. So far as we are 

 at present acquainted with the facts it appears possible to hold 

 either of the two following views with respect to the sequence 

 generally : — 



Firsts that the observed order is a naturally ascending one, hut 

 is more or less disguised by faulting, folding, and thrust-movements. 

 If this be so, and if further we assume that the igneous rocks of 

 the Eagle's jS'est repose on nearly the summit of the conglomerate 

 series, and that the quartzites and shales overlying the schists of 

 the Houghton Estate are the base, we have presented to us a group 

 of strata which, trusting only to the apparent dip, would seem to 

 be at least three miles in thickness. Moreover, this apparent 

 sequence of quartzites and shale, quartzites and conglomerate, sug- 

 gests an oscillating but gradually shallowing area of deposit. In 

 this case the basal conglomerates of the series may lie farther to 

 the north, and have yet to be discovered. 



Second, that the apparent order of the strata of the district is the 

 reverse of the true order. The quartzites, shales, and conglomerates 

 forming the Main Eeef Series will then be the highest, and will 

 represent the deep-water deposits, of which the coarser conglo- 

 merates composing the southernmost reefs are the shallow- water 

 equivalents. 



Which of these views is the nearer to the actual truth remains at 

 present an open question. So far, however, as our present know- 

 ledge goes, the conclusions to which the observations of the writer 

 within the typical district definitely point may be briefly stated as 

 follows : — 



(1) The gold-bearing conglomerates, together with the quartzites 

 and shales of the Witwatersrandt, form one definite geological 

 series ; but neither the base nor the summit of this series can 

 as yet be fixed. 



