Deposition of Gobi in South Afried. — Czyezkowski. 317 
the bottom of the fold will soon be reached. The section of 
the Ferreira gives the same impression. 
We may then inquire whether the considerable depths of 
which we have heard so much and to which the reefs are to 
descend are really to be attained. This question is ver} r im- 
portant, for in case of an upward turn in the formation at a 
workable depth, the entire wealth of the Rand may be extrac- 
ted. 
Taken as a whole the region is gently undulating and the 
area of high dip of the richest portion of the Rand which ex- 
tends over about fifteen kilometers is an exception. It may be 
explained by the later pressure undergone by the terrane by 
compression against the granite range situated north of 
Johannesburg. In general the strata are but slight^ folded 
at Randfontein, at Kleksdorp, at Modderfontein and at 
Heidelberg. 
The zone of Johannesburg alone is steeply inclined and its 
reefs were at first taken for true veins. It was a surprise, 
according to Mr. de Launay, when with increasing depths the 
reefs were seen to have a lower and lower dip and to conform 
perfectly with the position of the enclosing strata. We will 
add that it will be a still greater surprise when some day. 
perhaps very soon, the reefs are seen to rise toward the south 
in those mines where this change will occur at moderate depths. 
In short the structure of the Hand strata does not seem to be 
as yet well determined. All that we can say is that the Rand 
has been gently folded and that in the portions inclined more 
than the average such as the central regions of Johannesburg, 
the east-west trend characteristic of the hercynian chain of 
Europe is found plainly marked, as well in the gold bearing- 
strata as in the great diabase dyke of Klipriverslnirg. 
In this formation of schists, sandstones, quartzytes and con- 
glomerates of the Witwatersrand there are found a consider- 
able number of strata carrying more or less gold. These are 
the "reefs." The principal reel's so far recognized are as 
follows in ascending order: 
Preez's reel', or the Rietfontein group, exploited at Rietfon- 
tein. 
The main reef group, which includes the South reef. Main 
reef leader. Main reef and North reef. 
