64 PRESIDENTIAL ADDRESS SECTION B. 



No workable occurrence of wolframite has been found in 

 the Union, though the mineral occurs in association with cassi- 

 terite in certain of the mines of the Waterberg tin-fields, and in the 

 quartz-lodes on the farm Annexe Langverwacht, near Capetown. 



Lime. 



A recent survey* has shown that the Union has very 

 considerable resources of limestone, though the largest deposits 

 unfortunately are rather unfavourably situated with regard to 

 the principal industrial centres. 



The most important occurrence being worked at the present 

 time is that near Taungs, which is estimated to contain 7,000,000 

 tons of high-grade limestone. There is also a considerable 

 deposit near Potgietersrust, in which the limestone has resulted 

 from the de-dolomitisation of the normal dolomite of the Trans- 

 vaal system. f 



Pure cave limestone occurs in the Dolomite at many localities. 

 Until recently deposits of this type supplied the greater part of 

 the pure lime used in the cyanide works on the Witwatersrand, 

 and they still make an important contribution to the total output. 



Fairly considerable quantities of " blue " lime obtained from 

 "burning" ordinary dolomite, are produced at Irene, Olifants- 

 fontein, andjDther localities. It is used principally for building 

 purposes. 



Arenaceous surface-limestone is very largely employed for 

 the manufacture of cement. 



Rock Phosphate. 



There has now for nearly two years been a steady output of 

 crushed rock phosphate from the deposits at Saldanha Bay. These 

 are of great extent, $ readily accessible, and capable of being 

 cheaply worked ; and are without doubt destined to afford the 

 basis of a very important industry. The phosphate, an intimate 

 mixture of aluminium and iron phosphates, has been formed 

 mainly by the phosphatisation of granite and quartz porphyry 

 detritus, and to a less extent by the phosphatisation of these rocks 

 in situ. Though almost completely insoluble in ammonium citrate, 

 it has practically demonstrated that the phosphate, if finely 

 ground, has a very beneficial effect when applied together with 

 finely-ground lime to soils poor in phosphorus, and to sour soils; 

 the phosphorus being doubtless rendered assimilable by the agency 

 of soil bacteria. It was early realised, however, that its efficiency 

 as a fertiliser could be greatly increased by rendering the phos- 

 phoric acid more soluble and several processes to effect this have 



* Cf. Wybergh, W., and Du Toit, A. L. : The Limestone Resources of 

 the Union, Geological Survey Memoir, No. 11, Union of South Africa. 



t Cf. Young, R. B., Trans. Geol. Soc. S.A.. 1916. p. 57. 



+ Cf. Du Toit, A. L. : Report on the Phosphates of Saldanha Bay. 

 Memoir No. 10, Geological Survey, Union of South Africa. 



