170 Journal op the Department of Agriculture. 



REPRESENTATIVE TRANSVAAL SOILS. 



II. 



Pretoria Quartzite Sandy Soils. 



Bv B. J. Smit, B.A., Division of Clieniistiy 



Occurrence. — Tlie soils classed under tlic al)ove lieadiuj;' ocliu' in 

 ilie I'retoria, Krugersdorp, a'.J(l Witwateisvaiid Distiirts, and jjiobably 

 Avherevei- outcrops of tlie beds of the Mag-aliesberg", ])aspoort, and 

 Timeball Hill quartzites appear. 



The outcrops of these three quartzites of the Pretoria series form 

 three distinct ranges of hills in the Pretoria District, south and north 

 of the tovTU. On the south is the Timeball Hill range, immediately 

 north the Daspoort range, and farther north the Magaliesberg range. 

 The intervening hollows consist chiefly of shales aiid intrusive igneous 

 rocks. The Pretoria series \vith these quartzites run tJirough many 

 districts in the Transvaal, and generally speaking the Magaliesbeig 

 and Dasi)oort quartzites are the most imjjortant as regards the forma- 

 tion of the typical quartzite soils, since the beds are thicker than is 

 the case witli the Timeball Hill beds, presenting a larger area from 

 which the soil type under discussion is formed. The Magaliesberg 

 quartzites form, almost wherever the Pretoria series occur, the 

 broadest quartzite outcrop of the three. The Timeball Hill outcrops 

 again consist mainly of bands of quartzites witli shales and Jiaematite 

 or some other iron ore, so that the true type of quartzite 

 soil is best developed on or near the Magaliesberg quartzites. The soils 

 formed from these beds ■;ire often influenced to some extent by the 

 neighbouring shales and diabase. The actual samples discussed in 

 this paper were obtained from the three districts mentioned above, and 

 the analysis of at least one sample from each of the three quartzite 

 horizons, Magaliesberg, Daspoort, and Timeball Hill is quoted. 



Nature and Origin. — The quartzite soil is a red or brown to light- 

 grey very sandy soil, and is derived from the quartzite rocks which 

 consist chiefly of quartz grains cemented together with silica. These 

 rocks sometimes contain muscovite and nearly always some iron ore to 

 which the led colour of many of the quartzite soils is due. Some 

 quartzite rocks are almost white, and give rise to a light-grey soil, 

 Avliich may gradually, with the accumulation of organic matter, 

 become a darker colour. The quartzite being a sedementary rock 

 consists of particles which have previously to being cemented 

 together undergone denudation, and with the subsequent disintegra- 

 tion of the rock, and formation of the soil, they suffer a further 

 reduction in size, giving finally a soil in wliich there are hardly any 

 stones (by stones are meant those particles which are larger than 

 o mm. in diameter) and only a very small proportion of fine gravel 

 (particles greater than 1 and less than 3 mm. in diameter). On 

 dividing the sand and tine gravel into grades it is found that the 

 soil consists for tlie greater part of particles between 1 and ^ mm. in 

 diameter. The average of 12 quartzite soils gave 69 per cent, of 

 particles between 1 and ^ mm. in djamcter. 



