Address by Dr. Hahn. 45 



A somewhat analogous formation is observed in the numerous caves- 

 found on that grand block of mountains between Worcester and the 

 Bokkeveld. In nearly all these caves occurs Bat guano, and below 

 the guano on the bed rock is generally found a stratum of white 

 crystalline saline matter, composed of two or three compounds,, 

 which can be separated by fractional solution and crystallization. 

 j.iiey are Phosphates of Ammonia and Potash. Now, these phos- 

 phatic deposits of the caves throughout South Africa also call for 

 investigation are the products of the disintegration of Doleritic and 

 under the heading of Mineral Chemistry. 



Closely connected with the analyses of minerals are those 

 investigations which are directed to the composition of soils, and 

 which are undertaken more with a view to a practical object. We 

 cannot withhold our recognition from the work which has been under- 

 taken and carried on in the Agricultural Department in connection 

 with the investigation of soils of the Colony. They were first under- 

 taken on the coast and grain districts of the Colony ; that is to say, of 

 those districts in which the soil consists of the products of the dis- 

 integration of metanidrphous slates, sandstones, and intrusive granite, 

 Malmesbury, Paarl, Stellenbosch, Cape, and Caledon. The results 

 of these investigations are, so far as they have gone, of eminent 

 importance for the various branches of agriculture, and these results 

 should now be turned to use. The mere analyses of the soils are 

 of little immediate use. The value of these analyses depends upon 

 their correct interpretation and upon their application to practice. 

 The numerous results of these investigations most definitely prove 

 that all the primary soils formed of the previously mentioned rocks, 

 viz., metamorphous slate, sandstone, and granite are poor in all the 

 essential constituents of plant food, more particularly in lime. The 

 amount of Phosphoric Oxide is very low ; only Potash occurs in such 

 quantity that crops requiring Potash may be cultivated with advan- 

 tage, such as the vine, grain, and potatoes. The leguminous 

 plants, clover and lucerne, and also tobacco, do not find in this 

 soil sufticient plant food, especially lime, for a healthy and luxuriant 

 growth. We know that lime is an indispensable constituent of plant 

 food, that it is specially accumulated in old leaves, in bark, in wood, 

 whilst potatoes, carrots, and also grain, and those young parts of 

 plants in which the vital functions are most active, buds, young 

 shoots, and young leaves do not contain or require a larger supply 

 of lime. Whilst wheat (grain) takes of one hectare 1.04 kilograms of 

 lime, and potatoes (tubers) 4.19 kilograms of lime, the same area 

 loses through cultivation of clover 11 1.8 kilograms, and through 

 tobacco 153.7 kilograms (Ehermeyer, Chemie der Pflanzen). These 

 latter were already called by Liebig lime plants. This great 

 scientist also recognized the fact that the specific physiological 

 functions of one mineral constituent in this system of plants could 

 not be performed by another, and that these lime-requiring crops 

 do not thrive on soil poor in lime. Of still greater importance are 

 these investigations into the soils of the Western Province for 

 Forestry and Arboriculture. All kinds of trees grown in the forests 



