157 

 PART V. GEOLOGICAL RELATIONS AND PLANT FOOD. 



When these soil investigations were commenced the work of the Geo- 

 logical Commission had not advanced to the stage it has now attained, 

 and the results of that work were not available, as they are at present, 

 for the purposes of our own investigation. The Geological survey of the 

 Colony cannot but be of great worth to the scientific agriculturist, tihe 

 more so when supplemented by investigations such as these; in fact, it is 

 not too much to say that, in great part, it becomes thus fully valuable 

 only when so supplemented. The detailed and instructive maps issued 

 by the Geological Commission, showing, in very many cases, the 

 boundaries of the farms surveyed, cover largely the ground traversed by 

 the chemical staff, and are comparable with the maps issued by my own 

 office, in connection with which it has ever been the endeavour to mark, 

 as accurately as possible, the farm boundaries and all localities whence 

 samples of soil have been collected. Hence the soils analysed can often 

 be assigned to their proper geological formations, and deductions can be 

 drawn accordingly. Facilities were thus afforded whereby it became pos- 

 sible to arrange the figures in the subjoined tables in classified lists. 



Before any further reference is made to these figures, the extreme 

 difficulty of obtaining samples of soils typical of definite geological forma- 

 tions must be mentioned. It does not need much discernment to classify as 

 a Table Mountain series soil one taken from the top of Table Mountain, or 

 as a Malmesbury series soil one from the upper slopes of Lion's Rump. 

 But when a valley composed of beds of the Bokkeveld series is> flanked 

 by sandstone mountains, it becomes less easy to predicate to what extent 

 each has influenced the chemical nature of the soil ; still more complicated 

 is the problem when dealing with such districts as Robertson, where, in 

 parts, quite a large number of rocks contribute to the formation of the 

 soil. 



Had the samples of soils examined been so selected as specially to 

 typify certain definite geological series, it is highly probable that ere now 

 much more would have been learnt regarding the nature from the 

 farmer's standpoint of the soils derived from each of these series; but 

 circumstances have all along rendered any such system of collection im- 

 practicable; indeed, geographical rather than geological considerations 

 perforce ruled the selection of areas to be investigated. 



In spite of the fact that conditions were not propitious for the selec- 

 tion of typical samples, it has been possible to sort out from the many 

 soils that have been analysed some to typify various geological forma- 

 tions, and the chemical composition of the soils so sorted out on the 

 whole bear out the reasonableness of the classification. For the purpose 

 of these comparisons only analyses conducted by the standard method 

 adopted in our laboratories have been made use of. 



I propose, first of all, to consider the soils derived from the geolo- 

 gically oldest rocks, and to follow the upward sequence thence, as circum- 

 stances permit, ending with the superficial deposits. 



Beginning, then, with the pre-Cape rocks, as the Geological Com- 

 mission has termed them, which underlie the Table Mountain and corre- 

 lated series, the soils derived from the Malmesbury series require first 

 notice. No analyses, performed by the standard method, of sufficiently 

 typical soils collected within the Division which gives its name to this 

 geological series, are available, but from the Malmesbury beds of the 

 Cape, Paarl, and Stellenbosch Divisions, the sixteen soils enumerated 

 below were taken, in such places as to be practically representative. The 

 series of rocks from which these are derived consists mostly of hard, close 

 clay slates; the chemical composition of the latter is, for the most part, 



