Lysurn—WMining and Minerals in the Transvaal, ete. 17 
The question of maximum workable depth arises in connexion 
with the deep levels of the Randt. In connexion with this ques- 
tion it may be learned from the State Reports that experiments 
have been made on the property of the Robinson Deep-Level Gold 
_ Mining Company. The observations were made in a shaft 2067 
feet deep, which was not connected with any other shaft on the 
estate. The result gave a rise of 1°C. in temperature for every 
492 feet, say (1° C. for 150 metres), the ordinary rate of increase 
being in EKurope and America 1° C, for 30 to 31 metres. 
Experiments were also carried out on the Langlaagte 
Company’s property, the depth of the shaft being 1083 feet, 
resulting in demonstrating a rise of 1° C. for each 300 feet 
(or 1°C. for 92). 
Taking 5000 feet as a limit to which working can actually be 
pushed, and considering it, in view of the less favourable of the 
above-mentioned experiments, viz. that of the Langlaagte Deep, 
it would appear that the total increase of temperature to be ex- 
pected would not exceed 17° C. at 5000 feet, which, added to the 
temperature at the top of the shaft, in this case 20° C., would bring 
the temperature, which the worker would be exposed to, up to 
a7 C., equivalent to 98° F., a temperature which would in no 
practical way impede mining operations. The fact is to be borne 
in mind that these tests were carried out in shafts, entirely dis- 
connected from any other. 
The result of connecting shafts would undoubtedly be a lower- 
ing of temperature in both. 
Judging by the above data it will be reasonable to infer that 
mining operations can be carried on, in these countries, to a very 
great depth. As bearing on the geology of the country and the 
working of the reefs, attention should be called to the faults occur- 
ring in the Randt which are either of the ordinary class or of the 
class of fault known as the “ overthrust fault,” and called in 
Hurope “ reversed fault.” ‘lhe existence of these faults will largely 
influence enterprise in the future, in deep levels (Plate 11.). 
On the property of the Witwatersrandt Gold Mining Company, 
two outcrops of the Main-reef series are known to exist. ‘The reef 
series has been thrown up by an overthrust fault, the fault-plane 
being filled up by dyke matter, viz. dolerite. This at first gave 
rise to considerable speculation, many mining men believing it to 
C 
SCIEN. PROC. K.D.S., VOL. IX., PART I. 
