Fertility of some Colonial Soils. 23 



they approach the Bokkeveld soils in respect of their potash content. 

 This feature is perhaps better distinguished on taking the averages, 

 which, for the last table, are as follows : — 



Lime -042 



Potash -141 



Phosphoric oxide "075 



If these were simply Bokkeveld soils diluted by alluvial sand 

 from the Table Mountain series one would expect a lowering of all 

 three plant-food constituents in the same proportion ; but, as we 

 see, the reduction of lime and phosphoric oxide is proportionately 

 much greater than that of the potash.'''' It puzzled me at first to 

 account for this, but one explanation seems feasible. Dr. Corstor- 

 phine, in his second report on the Geological Survey of the Colony, f 

 remarks on the distinctive character of the lowest beds of the 

 Bokkeveld series, which enables one with little or no difficulty to 

 draw the line of separation between it and the Table Mountain 

 series below. The basement beds of the Bokkeveld series, he says, 

 are felspathic and micaceous, and quite different from the hard, 

 compact quartzite of the older series. I am not aware whether 

 it is potash felspar that is here alluded to, and our analyses, as 

 before observed, do not furnish data with regard to the total amounts of 

 the plant-food constituents in the soil, but it seems just possible that 

 in this fact lies the explanation of the predominance of potash in 

 what appear to be primary soils collected near the common horizon 

 of the two series. It would certainly be of interest to investigate 

 the subject more closely, so as to confirm or disprove the hypothesis 

 here suggested. For this purpose samples of soil would have to be 

 collected in such a manner as to render it absolutely certain that 

 they were primary soils representing the vicinity of the line of 

 junction ; in the past the collection of soils has been carried on 

 largely without regard for geological considerations — the time has 

 now arrived, I think, for greater precision in this respect. 



It may be pointed out just here that one of the soils classed as a 

 true Bokkeveld soil. No. 119 in Table VIII., bears a considerable 

 resemblance in chemical composition to those enumerated in 

 Table IX. : its potash, compared with the deficiency of lime and 

 phosphoric oxide, is high, but not so high as the general run of true 

 Bokkeveld soils, and in both lime and phosphoric oxide it is the 

 poorest of the Bokkeveld soils. I have classed it among the latter 



* In a mixture of 45 parts of the average Sandstone soil (Table YII.) with 55 

 of the average Bokkeveld soil (Table VIII.), the percentages of plant food would 

 be — Lime, -228; Potash, -141; Phosphoric oxide, '081. 



f Ann. Eept. Geol. Commission, 1897, p. 16. 



